Dissertations / Theses on the topic 'Ferromagnetic resonance'
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Marcham, Max Ken. "Phase-resolved ferromagnetic resonance studies of thin film ferromagnets." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3882.
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Precessional dynamics are exploited in the operation of high frequency magnetic devices such as magnetic disk drives, non reciprocal microwave devices and spin transfer oscillators. The trajectory of the precession and its damping are of crucial importance. This thesis presents the characterisation of a variety of magnetic thin film structures performed with a range of phase sensitive techniques. It is possible to obtain new insight by utilising the chemical and site specificity of X-ray Magnetic Circular Dichroism (XMCD) to isolate the precession in different chemical species or at distinct sites in the crystal structure of a chosen material. X-ray Ferromagnetic Resonance (XFMR) combines XMCD and Ferromagnetic Resonance (FMR) phenomena in a technique capable of measuring the FMR response of an alloy or multilayer with both chemical and site specificity. To complement the XFMR technique a low temperature Time-Resolved Magneto Optical Kerr Effect (TR-MOKE) setup has been developed. This allowed for the characterisation of samples at temperatures in the range 4 K to room temperature. A frequency swept Vector Network Analyser FMR (VNA-FMR) setup was developed to allow for a fast method for determining the resonance condition and damping of a range of ferromagnetic thin film samples. In addition a TR-X-ray Photoemission Electron Microscopy (TR-XPEEM) setup has been established which allows images to be obtained with magnetic contrast. The combination of the above techniques has lead to studies on rare earth capped spin valve free layers and the measurement of spin pumping in industrially relevant spin valves.
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Kim, Jongjoo. "Localized Ferromagnetic Resonance using Magnetic Resonance Force Microscopy." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1222191966.
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Lee, Inhee. "Nanoscale Ferromagnetic Resonance Imaging using Magnetic Resonance Force Microscopy." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1281111992.
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Inkoom, Godfred. "Ferromagnetic Resonance of LSMO Thin Film." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12933.
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The magnetic properties of a 15uc thick LSMO thin film on SrTiO3 (STO) substrate atT=150K was investigated using the technique of ferromagnetic resonance (FMR). The FMRmeasurement of the 15uc thick LSMO thin film at a frequency f = 9.75GHz and powerP = 0.6325mW as a function of the angle between the static magnetic field H, and theeasy direction of magnetization within the sample plane in the "in-plane" (IP) configuration displayed an FMR spectrum. This resonance spectrum shows unequal resonance field peaks. The unequal peaks in the resonance field may be attributed to the uniaxial anisotropy field which satisfies the conditions for ferromagnetic resonance. The unequal peaks in the resonance field shows a maximum and minimum with negative and positive curvature which either increases or decreases with respect to the resonance field respectively. This increase or decrease in the resonance field depends on the magnetization direction. It has been shown that for a thick 15uc LSMO thin film at T = 150K the center position and the full width half maximum (FWHM) of the resonance field were 1070.1875 Oe and 159.3125 Oe respectively.
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Bataiev, Yurri N. "Ferromagnetic Resonance Study of Spintronics Materials." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1236192587.
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Denysenkov, Vasyl. "Broadband Ferromagnetic Resonance Spectrometer : Instrument and Applications." Doctoral thesis, KTH, Microelectronics and Information Technology, IMIT, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3602.
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This thesis compiles results of research in two mutuallydependent parts: 1) development of ferromagnetic resonance(FMR) spectrometer to study microwave properties offerromagnetic materials, and 2) characterization of new irongarnets: pulsed laser deposited Y3Fe5O12and Bi3Fe5O12films and Ce:Y3Fe5O12single crystal.
First part describes a novelBroadbandFMRSpectrometerdesigned to characterize thin ferromagneticfilms. The spectrometer uses two probeheads: one is the X-bandmicrowave reflection cavity for room temperature measurementsand the in-cryostat microstrip line probe to perform FMRexperiments in the frequency range from 50 MHz to 40 GHz. Veryuniform and stable magnetic field up to 2.4 T, temperatures 4 Kto 420 K, and continuous frequency scan performed byHP8722Dvector network analyzer provide various modes ofoperation. Both probeheads are equipped with two-circlegoniometers to ensure accurate study of magneticanisotropy.
The spectrometer was used to make express-analysis ofquality thus to optimize processing parameters of epitaxialiron garnet films grown by pulsed laser deposition (PLD).Comprehensive study of uniaxial and cubic magnetocrystallineanisotropy has been performed for Ce:Y3Fe5O12bulk crystal as well as for Y3Fe5O12and Bi3Fe5O12films grown on different substrates by PLD andreactive ion beam sputtering techniques. BroadbandFMR-spectroscopy revealed difference in spectra of domain wallresonances: instead ofsoftspin modes in filmsgrown by liquid phase epitaxy, PLD-made films showdiffusetransformation of domains near thesaturation field. This effect indicates non-uniformity ofsaturation magnetization and field of uniaxial anisotropy inPLD-iron garnets. Spin wave resonances in comparison withuniform FMR have been studied to evaluatelocalqualityof ferromagnetic films. The resonance field andFMR linewidth behavior were studied at various crystallographicdirections determined by X-ray diffraction.
FMR was used to choose PLD-made YIG films with low losses atmicrowave frequencies and to build magnetostatic surface wavesmicrowave bandpass filter. The filter was designed as a planarfilm structure with a microstrip line for transducers. It is afirst demonstration of feasibility to introduce PLD processingtechnique to magnetostatic wave technology.
Magneto-optical study of Ce:Y3Fe5O12single crystal complements results ofFMR-spectroscopy of new garnets.
Keywords:ferrites, thin films, ferromagnetic resonance,microwaves, FMR spectrometer, magnetic anisotropy,magnetostatic waves.
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Adams, Daniel J. "Ferromagnetic Resonance Studies of Coupled Magnetic Systems." ScholarWorks@UNO, 2016. http://scholarworks.uno.edu/td/2121.
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The high-frequency properties of coupled magnetic systems have been investigated using vector network analyzer ferromagnetic resonance (VNA-FMR) spectroscopy. SAF structures consist of two ferromagnetic layers separated by a non-magnetic spacer, coupled through the indirect exchange interaction. The ferromagnetic layers of our samples were composed of FeCoB separated by a layer of Ru. The thickness of Ru was varied in the range of 8 to 18 Å among the samples studied. Antiferromagnetic coupling can be quickly identified by the major hysteresis loop (MHL).
A new way of displaying FMR data for these trilayer samples is presented which completely preserves the anisotropy effects while fully characterizing the angular dependence of FMR. The advantage of our representation is that the high-frequency data can be easily compared to the static switching behavior at any angle obtained through susceptibility measurements.
Ferromagnetic resonance; Coupled; Synthetic antiferromagnet; Magnetization switching
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Khazen, Khashayar. "Ferromagnetic resonance investigation of GaMnAs nanometric layers." Paris 6, 2008. https://tel.archives-ouvertes.fr/tel-00329331v2.
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Cette thèse est dédiée à l’étude des propriétés magnétiques des couches nanométriques de GaMnAs par Résonance ferromagnétique (RFM). Trois séries des échantillons sont étudiées afin d' élucider l’influence des contraintes, la concentration des trous et la concentration de manganèse, sur les propriétés magnétiques de GaMnAs. Dans la première série, les échantillons de Ga1-xMnxAs avec x=0. 07 déposés sur les substrats de GaAs (en compression) et GaInAs (en extension) sont étudiés. Les résultats des mesures de l’aimantation, la résistivité et l’effet de Hall sont présentés. Les axes faciles de l’aimantation et le type d’anisotropie sont déterminés par mesures RFM. Les variations angulaires des spectres RFM sont étudiées en détails et le facteur g, la température de Curie et les constantes d’anisotropie sont déterminées en fonction de la température. La résonance des ondes de spin sont également observées et interprétées. Les observations sont comparées aux modèles phénoménologiques proposés et le spin stiffness et l’intégrale d’échange entre les ions de manganèse sont déduits. La deuxième étude concerne une série des échantillons de GaMnAs avec même niveau de dopage de Mn de 7% concentration atomique dont les concentrations de trous étaient variées via la passivation par l’hydrogène. Les concentrations des trous sont déduites des mesures d’effet Hall sous la condition de forts champs appliqués et à très basses températures. Les concentrations de trous mesurés correspondent aux différents régimes de conductivités ; de régime isolant aux régimes bande d’impureté et métallique. Les échantillons sont caractérisés par magnétométrie SQUID et les mesures de résistivité. L’aimantation en fonction de la concentration de trous est comparée aux prédictions du modèle RKKY. Les mesures de ERDA sont appliquées à la fin de déterminer la concentration de hydrogène dans l’échantillon ferromagnétique avec la concentration de trous la plus faible dans la série. La structure des domaines de cet échantillon est étudiée par microscopie magnéto-optique d’effet Kerr. Les spectres RFM sont analysés en détail et la concentration de trous correspondant à la formation de l’ordre ferromagnétique est estimée à 1019cm-3. Les facteurs g dépendent de la concentration de trous et la température. La relation entre les facteurs g et les polarisations de trous des échantillons calculées théoriquement est présentée. L’étude d’anisotropie des échantillons est fournie la détermination des constantes d’anisotropie magnétocrystallines en fonction de la concentration de trous et la température. Leurs variations sont comparées aux modèles théoriques. Les surfaces d’énergie sont déduites des constantes d’anisotropie magnétocrystallines mesurées, sont calculées en fonction de l’aimantation et les orientations et les grandeurs du champ appliqué. L’influence d’augmentation du niveau de dopage, de 7% à 21% concentration atomique est étudiée dans la troisième série des échantillons. Contrairement des prédictions théoriques, la température de Curie n’est pas augmentée en dessous de 180K. Les paramètres de RFM sont comparés à ceux des échantillon standard de GaMnAs avec 7% concentration atomique de Mn. La raison est attribuée au haut niveau de la compensation magnétique. Les mesures sont également comparées aux prédictions théoriques basées sur les approximations de champ moyen. La relaxation de l’aimantation est étudiée en fonction des contraintes, la concentration de trous et Mn aussi bien que la température. Les constantes de damping, sont trouvées d’être anisotropes. Cette anisotropie, dépend fortement aux procès dont contribution est la dominante pour une configuration particulaire du systèmeThis thesis is dedicated to the study of the magnetic properties of GaMnAs nanometric layers by the ferromagnetic resonance (FMR) technique. Three series of samples have been studied to investigate independently the influence of the strain, the hole concentration and the Mn concentration on the magnetic properties of GaMnAs. In the first series, the Ga1-xMnxAs samples with x=0. 07, grown on GaAs (compressive strain) and GaInAs (tensile strain) substrates are studied. The results of magnetization, resistivity and Hall effect measurements are presented. From the FMR measurements the easy axes of magnetization and the type of magnetic anisotropy are determined. The angular variations of the FMR spectra are studied in detail and the g-factor, Curie temperature and the magnetocrystalline anisotropy constants are determined as function of temperature. Spin wave resonance were equally observed and interpreted. The observations are compared to the proposed phenomenological models and the spin stiffness and the exchange integral between the Mn ions are deducedThe second study concerns a series of GaMnAs samples with the same Mn doping level of 7% atomic concentration in which the hole concentrations was varied via a hydrogen passivation technique. The hole concentrations are deduced from Hall effect measurements in high fields and low temperatures. The measured hole concentrations correspond to different conductivity regimes from insulating to impurity band and metallic regimes. The samples are characterized by SQUID magnetometry and resistivity measurements. The magnetization as a function of hole concentration is compared to the predictions of the RKKY model. ERDA measurements are performed to determine the concentration of hydrogen in the ferromagnetic sample with the lowest hole concentration. The domain structure of this samples is investigated by magneto-optical Kerr effect microscopy. The FMR spectra are analyzed in details and the hole concentration corresponding to the onset of ferromagnetism is estimated to 1019cm-3. The g-factors depend on the hole concentration and temperature. The relation between the g-factors and the theoretically calculated hole polarization of the samples is presented. The anisotropy studies of the samples have provided the investigation of the magnetocrystalline anisotropy constants as a function of the hole concentration and the temperature. Their variations are compared to the theoretical models. The energy surfaces deduced from the measured magnetocrytalline anisotropy constants are calculated as a function of magnetization and applied field orientations and magnitudes. The influence of increasing the doping level from 7% to 21% atomic concentration is studied in the third series of samples. Contrary to the theoretical predictions, the critical temperature is not increased above 180K. The FMR parameters are compared to those of standard GaMnAs sample doped with 7%atomic concentration of Mn. The reason for no further increase in TC is attributed to high level of magnetic compensation. The measurements are also compared to the theoretical predictions based on the mean field approximations. The relaxation of the magnetization is studied as a function of strain, hole concentration, Mn concentration as well as temperature. The damping constants were found to be anisotropic. This anisotropy however depends strongly on the process whose contribution is dominant for a specific configuration of the system
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Kennewell, Kimberly. "Surface and interface anisotropies measured using inductive magnetometry." University of Western Australia. School of Physics, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0243.
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In this thesis, an inductive ferromagnetic resonance (FMR) technique is developed to measure the magnetisation dynamics in thin films across a wide range of frequencies and fields. In particular, this project concentrates on measuring higher order exchange dominated modes to observe surface and interface effects in bilayer films. The experimental technique was first developed as a time domain technique, utilising a fast rise time (~50 ps) step pulse to disturb the equilibrium position of the magnetisation. The subsequent precessional damped decay was measured at different applied fields to observe the resonant modes. The data is Fourier transformed to extract a frequency dependent susceptiblity, and results are presented for the frequency and linewidth dependence of excitations of a permalloy film as a function of applied field. This technique is limited to a frequency range dictated by the rise time of the pulse. The technique was then extended so as to use a continuous wave perturbation, utilising a network analyser as both the excitation source and the measurement device. The scattered wave parameters of both the transmission and reflection from the sample were measured, and a magnetic susceptibility is extracted. This method has a frequency range which is dictated by the bandwidth of the network analyser and the microwave circuit. In this project, results are presented for frequencies up to 15 GHz. The signal to noise ratio was also found to be lower than the pulsed technique. Fundamental resonant mode studies are presented for a Fe/MnPd exchange bias bilayer film. Crystalline and exchange anisotropies are extracted from angular measurements, and the behaviour of the magnetisation is investigated during its reorientation to a hard axis direction. Information about the distribution of the local exchange field strength and direction is predicted. Fundamental mode studies are also presented for a Py/Co exchange spring bilayer film. Two modes are observed, approximating an optical and acoustical excitation. Film systems were also designed with suitable thicknesses to observe in the experimentally available frequency range non-uniform exchange dominated excitations through the thickness of the film. The broadband nature of the experiment allowed the frequency of the modes to be measured as a function of field. Results from a single permalloy layer showed two observable modes, the fundamental and the first exchange mode. Measurements were also taken of bilayer films where permalloy is coupled to cobalt. In this system the effect of the cobalt is seen to shift the single layer Py mode frequencies, as well as introduce new modes. The relative intensities of the modes also change with the addition of cobalt. Results are shown for a Pt/Co multilayer coupled to a permalloy layer through a Cu spacer of varying thickness. The observation of excitations through the thickness of the film motivated the development of a suitable theory. A system of integro-differential equations were derived which account for dipole and exchange coupling in the film as well as the field screening by the metal of the coplanar line. The conductivity of the sample and the finite wavevector excitation of the stripline are also included. Numerical solution of the equations results in a spectrum of acoustical, optical and higher-order modes. Fitting of the model to the experimental results allowed extraction of the film parameters including; the exchange constants in the film; the surface pinning from any surface layer anisotropy; as well as the interlayer exchange coupling across the interface.
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Manuilov, Sergey. "Ferromagnetic resonance in films with growth induced anisotropy." Doctoral thesis, KTH, Integrerade komponenter och kretsar, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48248.
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This thesis discusses two different magnetic materials: epitaxial yttrium iron garnet (YIG) and heteromorphous CoFeB-SiO2 films. YIG films were grown by pulse laser deposition (PLD) techniques onto gadolinium gallium garnet (GGG) substrates of (111) and (001) crystal orientations. Using stoichiometric and overstoichiometric ablative targets, we developed two types of YIG submicron films. The films grown from overstoichiometric targets have magnetic properties slightly different from standard liquid phase epitaxy (LPE) YIGs. They also demonstrate good substrate matching and approximately 6% nonstoichiometry. In contrary, films grown from stoichiometric targets posses surprisingly high values of uniaxial anisotropy, meanwhile cubic anisotropy is reduced several times. These films also reveal strong lattice distortions and nonstoichiometry around 17%. Employing Weiss molecular field theory and single-ion anisotropy model we determined the preferential occupancy of the octahedral [a] positions in the YIG cubic lattices by Fe3+ vacancies. The vacancies were found to be preferentially oriented along the growth direction perpendicular to the film surface. We called this effect “deformation blockade”. Different magnetostatic surface wave (MSSW) filters were also demonstrated. The filters employ high uniaxial anisotropy in YIG submicron films with magnetic losses ΔH ~ 1 Oe. Heteromorphous CoFeB-SiO2 films were deposited onto glass substrates employing carrousel magnetron sputtering. This novel technique allows amorphous films fabrication with record high in-plane anisotropy. The induced anisotropy fields here are approximately dozen times greater the values achieved using conventional growth technique when external bias field is applied during deposition process. Interesting observations were made studying CoFeB-SiO2 magnetization dynamics in the wide frequency range from 500 kHz up to 15 GHz. Two different anomalies of the magnetic susceptibility were found at the field of in-plane anisotropy Hp and critical field Hcr (0 < Hcr < Hp). We explained the anomalies appearance by sequence of the domain walls transformations so that Néel-Bloch-Néel domain wall transition stands for the instability at H = ±Hcr and transition from the uniformly magnetized state to the domain state with Néel domain wall and vice versa is responsible for the instability at H = ±Hp.QC 20111122
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Unwin, Marion Elizabeth. "Broadband ferromagnetic resonance studies of magnetic recording media." Thesis, Keele University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414759.
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FMR spectroscopy is widely used for the characterization of many types of magnetic materials for use in an extensive range of applications. It is a powerful tool for probing both the magnetic properties and physical aspects of a material. In recent years in particular, there has been some interest in its use to study commercial recording media. However, there are a number of limitations inherent in the conventional method of observing FMR that restricts its usefulness and popularity as a research technique. The high, single frequency operation of the spectrometer makes broadband, frequency dependent measurements and studies of the unsaturated state of materials impractical. It also severely limits the quantity of data available making the analysis and interpretation difficult and prone to error. Additional complexities are encountered since the swept field technique means that a sample is subjected to a constantly changing magnetic environment which may not be ideal, especially for broad linewidth materials. A need, therefore, has been identified for an FMR technique capable of producing both swept field and swept frequency spectra over a wide range of frequencies. The design and development of a novel broadband FMR spectrometer is described in this thesis. The new technique has several advantages over similar methods presented in the literature. It can be applied over a very wide frequency range, dependent on the types of materials, for a variety of different FMR studies. The spectrometer itself is straightforward and easy to use and the resulting spectra (which show excellent agreement with equivalent conventional data) may be interpreted using the same models already used in FMR research. Most importantly, the simplicity of this spectrometer design means that it can be readily implemented in any reasonably equipped magnetics or microwave laboratory without the need for specific expertise or equipment. A preliminary broadband FMR study of magnetic recording media demonstrates the potential of the new technique both for more detailed characterizations of magnetic materials and for greater understanding of the ferromagnetic resonant effect itself.
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White, Shane Paul White. "Study of Heavy Metal/Ferromagnetic Films Using Electrical Detection and Local Ferromagnetic Resonance Force Microscopy." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524172007784423.
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Fang, Dong. "Current-induced torque driven ferromagnetic resonance in magnetic microstructures." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/241302.
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This Dissertation explores the interaction between the magnetisation and an alternating current in a uniform ferromagnetic system. Diluted magnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P) have been studied. Due to their strong spin-orbit coupling and well-understood band-structure, these materials are well-suited to this investigation. The combined effect of spinorbit coupling and exchange interaction permits the alternating current to induce an oscillating current-induced torque (CIT) on the magnetisation. In the frequency range close to the natural resonance frequency of the magnetic moments (gigahertz), CIT can excite precessional motion of the magnetisation, a process known as ferromagnetic resonance (FMR). CIT can be parameterised by an effective magnetic field. By analysing the lineshape of the measured FMR signals, the magnitude and orientation of this effective field have been accurately determined. Moreover, the current-induced fields in these ferromagnetic materials have been observed with symmetries of the Dresselhaus, and for the first time, Rashba spin-orbit coupling. A new class of device-scale FMR technique, named as CIT-FMR, has been established in this Dissertation, with the advantage of simple device structure (only a resistor is required) and scalability (measurements have been performed on devices sized from 4 μm down to 80 nm). This technique is not only limited to magnetic semiconductors, but can also be transferred to study other ferromagnetic systems such as ultrathin metal films. Finally, the CIT-FMR technique is employed to study the magnetic anisotropyin individual (Ga,Mn)As and (Ga,Mn)(As,P) micro-devices. Devices down to 80 nm in width have been measured in (Ga,Mn)(As,P), which show strong strain-relaxation-induced anisotropy, larger than any previously reported cases on (Ga,Mn)As. Furthermore, due to the tensile-strain on the (Ga,Mn)(As,P) epilayers, the anisotropy field due to patterning-induced strain-relaxation in these devices is observed to take the opposite direction compared to that in the compressively-strained (Ga,Mn)As samples.
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Körner, Michael. "Morphology-Induced Magnetic Phenomena Studied by Broadband Ferromagnetic Resonance." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-127005.
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In the present work, the influence of the morphology of thin ferromagnetic films on their static as well as dynamic magnetic properties was investigated by means of broadband ferromagnetic resonance (FMR). Using an ion beam erosion process the surface of the substrates was periodically modulated (ripples), where the modulation wavelength is determined by the ion energy. In this way a well-controllable roughness profile evolves ranging from a few ten up to several hundreds of nanometers in wavelength. The substrate’s surface profile in turn is repeated by films grown on top offering an easy and fast approach to investigate morphology influences on the magnetic properties. This work aims on modifications of the magnetic anisotropy as well as the FMR linewidth of the magnetic relaxation process. Prior to magnetic investigations the existing FMR setup was extended to measure FMR spectra at a fixed microwave frequency while sweeping the external magnetic field. Furthermore, a software toolbox was developed to perform the data processing and evaluation. Starting with the morphology influence on the magnetic anisotropy 10 nm thin Fe, Co, and Ni81Fe19 (Permalloy ≡ Py) films were deposited on rippled Si substrates. Due to Si displacements during ion erosion and natural oxidation the rippled Si substrates exhibit an amorphous surface causing a polycrystalline material growth. This leads to a suppression of magneto-crystalline anisotropy leaving only morphology-induced anisotropy contributions. Here, a uniaxial magnetic anisotropy (UMA) was observed that aligns its easy axis with the ripple ridges, whereas its strength decays with increasing ripple wavelength for all materials. From thickness-dependent measurements two characteristic regions were determined with competing uniaxial volume and surface anisotropy contributions. Underlined by micromagnetic simulations a dominant volume contribution was found in the thin region accompanied by magnetic moments nearly following the surface corrugation. In the thick region the UMA is controlled by dipolar stray fields at the surface. In contrast to Si, ion eroded MgO keeps its crystal structure offering epitaxial growth of 10 nm thin single-crystalline Fe films. Consequently, a superposition of morphology-induced UMA and magneto-crystalline cubic anisotropy was observed. The direction of the ripple ridges is predetermined by the incident ion beam, which allows to freely orient the UMA’s direction with respect to the cubic anisotropy, offering a possibility for anisotropy engineering. In comparison to the planar reference case rippled magnetic films exhibit lower intrinsic and extrinsic relaxation contributions. For the final part, 30 nm Py was grown on rippled Si covering modulation wavelengths λ ranging from 27 to 432 nm. Using magnetic force microscopy and holography measurements the dipolar stray fields above and inside the magnetic layer were characterized. For λ ≥ 222 nm, the stray fields act as scattering centers for spin waves triggering two-magnon scattering (TMS). This causes an apparent line broadening generating distinct peaks in the frequency-dependent linewidth whose position can be tuned by altering λ. These effects are understood in the framework of a perturbation theory of spin waves in periodically perturbed films recently presented in the literature. Furthermore, the in-plane angular dependence of the linewidth revealed a two-fold symmetry, which is not present for vanishing TMS at small λIn Rahmen dieser Arbeit wurde der Einfluss der Morphologie eines dünnen ferromagnetischen Films auf dessen statische und dynamische Eigenschaften mittels breitbandiger ferromag- netischer Resonanz (FMR) untersucht. Durch Ionenstrahl-Erosion wurde die Oberfläche des verwendeten Substrats periodisch moduliert (Ripple), wobei die Wellenlänge der Modulation durch die Ionenenergie bestimmt ist. Dies ermöglicht die kontrollierte Herstellung rauer Oberflächen mit Wellenlängen zwischen wenigen zehn bis zu einigen hundert Nanometern. Werden auf diesen Oberflächen Filme abgeschieden, übernehmen diese die Modulation. Somit ergibt sich eine einfache und schnelle Untersuchungsmöglichkeit der magnetischen Filmeigenschaften in Hinblick auf die Morphologie. Das Ziel dieser Arbeit ist die Untersuchung von Morphologieeinflüssen auf die magnetische Anisotropie sowie FMR-Linienbreite. Im Vorfeld der magnetischer Untersuchungen wurde der bestehende FMR-Aufbau um einen Messmodus erweitert, sodass Messungen bei fester Mikrowellenfrequenz und gleichzeitigem Durchfahren eines externen magnetischen Feldes möglich wurden. Weiterhin wurde ein Softwarepaket für die Datenauswertung entwickelt. Beginnend mit dem Morphologieeinfluss auf die magnetische Anisotropie wurden 10 nm dünne Fe, Co und Ni81Fe19 (Permalloy ≡ Py) Filme auf periodisch moduliertem Si abgeschieden. Durch Versetzungen während der Ionenstrahl-Erosion und Bildung einer natürlichen Oxidschicht bildet sich bei den verwendeten Substraten eine amorphe Oberfläche, was zu polykristallinem Schichtwachstum führt. Dadurch wird die magneto-kristalline Anisotropie unterdrückt und morphologie-induzierte Beiträge bestimmen die Anisotropie. Beobachtet wurde eine induzierte uniaxiale magnetische Anisotropie (UMA), deren leichte Richtung sich entlang der Ripple-Wellenzüge ausrichtet. Mittels schichtdickenabhängigen Messungen wurden zwei charakteristische Regionen mit konkurrierender uniaxialer Volumen- und Oberflächenanisotropie ermittelt. Dabei ist die Volumenkomponente im Bereich dünner Schichten vorherrschend und die magnetischen Momente richten sich entlang der Oberflächenmodulation aus. Für dickere Schichten ist die UMA dahingegen durch dipolare Streufelder bestimmt. Die experimentellen Funde werden in beiden Bereichen durch mikromagnetische Simulationen untermauert. Im Gegensatz zu erodiertem Si behält MgO seine Kristallstruktur, was epitaktisch gewachsene, einkristalline Fe-Schichten von 10 nm Dicke ermöglicht. Folglich wurde eine Überlagerung aus induzierter und kristalliner Anisotropie beobachtet. Dadurch, dass die Richtung der Ripple durch die Richtung des Ionenstrahls während der Erosion vorgegeben wird, lässt sich die UMA frei gegen die kristalline Anisotropie drehen, was wiederum Möglichkeiten zur gezielten Beeinflussung der Anisotropie bietet. Im Hinblick auf die dynamischen magnetischen Eigenschaften führen Ripple zu einer Verringerung der intrinsischen und extrinsischen Relaxationsbeiträge. Für den letzten Teil der Arbeit wurde 30 nm dünnes Py auf Si-Ripple gewachsen, wobei ein Wellenlängenbereich von λ = 27 nm bis 432 nm abgedeckt wurde. Mit Hilfe von magnetischer Kraftmikroskopie und Holographie wurden die dipolaren Streufelder über und in den Filmen untersucht. Ab λ ≥ 222 nm ermöglichen diese dipolaren Felder eine Streuung von Spinwellen, sodass Zwei-Magnonen-Streuung (TMS) auftritt. Dies führt zu einer scheinbaren Linienverbreiterung und äußert sich durch einzelne Peaks in der frequenzabhängigen Linienbreite. Letztere lassen sich in ihrer Frequenzposition durch die Wellenlänge des Substrates beeinflussen und können mittels einer kürzlich in der Literatur veröffentlichten Störungstheorie für Spinwellen in periodisch gestörten Filmen erklärt werden. Weiterhin wurde in der winkelabhängigen Linienbreite eine zweifache Symmetrie beobachtet, welche durch die TMS hervorgerufen wird und folglich nicht bei kleinen Wellenlängen zu beobachten ist
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Peterman, Derrick W. "Control of chaos in thin films at ferromagnetic resonance /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu148793458997678.
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Wheeler, May Catherine. "Manipulation of fullerene C60 spintronic devices via ferromagnetic resonance." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/8258/.
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C60 has been included in hybrid magneto-molecular devices as an active layer where the C60 is thermally sublimated under high vacuum and the metals are sputter deposited in-situ. Multilayer C60/Co samples were measured by x-ray reflectivity and transmission electron microscopy to show that there is little interdiffusion of layers suggesting C60 is robust to the deposition of metals by sputtering. We have observed 25% magnetoresistance through 60 nm of C60 at 10 K as well as 8% magnetoresistance at room temperature through 20 nm of C60. Unexpected asymmetric effects in external magnetic field were observed in some C60 spin valves as a result of interfacial hybridisation between C60 and ferromagnetic materials. It has also been shown that when C60 is in contact with a ferromagnetic material, spin polarised electrons from the ferromagnet are transferred into the C60 as a result of differences in chemical potential. This has been measured in C60/Co and C60/Py bilayer samples and observed via ferromagnetic resonance and point contact Andreev reflection. The molecular properties of C60 can be manipulated by an adjacent ferromagnetic material at ferromagnetic resonance dissipating energy into the C60. This changes the frequency/energy of molecular vibrations, as well as an enhanced photoemission from the C60. The changes can be correlated to spin pumping and phonon injection. The conductivity through a C60 layer is also increased during ferromagnetic resonance of the adjacent Py by up to 8% owing to increased phonon-assisted hopping steps.
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McCullian, Brendan Andrew. "Detection of Ferromagnetic Dynamics Using NV Centers in Diamond." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1585664864822124.
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Ma, Changlin. "Ferromagnetic resonance studies of DC magnetron sputtered CO-CR films." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26444.
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The X-band FMR has been employed to investigate the angular variation of resonance Fields of DC sputtered Co-Cr Films with different substrate temperatures. This angular variation has been Fitted with the classical uniaxial
anisotropy crystal model and yields the values of 2K₁/M-4πM=-4∼-7 KOe,
4K₂ =-0.8∼0.8 KOe and g-factor = 2.3~2.8. The FMR measurments of the first anisotropy constant are quite different from the counterparts measured with VSM. This discrepancy is interpreted as a result of the formation of two ferromagnetic phases. With this simple model, the substrate temperature dependence of First anisotropy is explained and it is predicted that a lower substrate temperature will improve the Co-Cr Films for their potential application in perpendicular magnetic recording devices. The angular dependence of the FMR linewidth is discussed.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Sherratt, Sarah L. "Characterisation of iron oxide corrosion products using impulse ferromagnetic resonance." Thesis, Keele University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.518314.
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Burgei, Wesley Alan. "Ferromagnetic Resonance Study of Square-Array Antidot Permalloy Thin Films." Miami University / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=miami1059192138.
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Du, Chunhui. "Probing Spin Dynamics and Transport using Ferromagnetic Resonance based Techniques." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437066082.
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O'Dell, Ryan Andrew. "Resonant Ferromagnetic Absorption and Magnetic Characterization of Spintronic Materials." University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1533043360679487.
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Braybrook, Julian Hugh. "Effects of paramagnetic and ferromagnetic particles on magnetic resonance (MR) imaging." Thesis, University of Cambridge, 1989. https://www.repository.cam.ac.uk/handle/1810/250949.
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Ofstad, Johannes. "Ferromagnetic Resonance Spectroscopy Studies of Permalloy/Copper/Chromium/Copper thin films." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-24417.
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A theroretical and experimental study of 10Py/10Cu, 10Py/10Cu/xCr/10Cu (with x=4,7, 10,13 nm) thin films has been performed. The thin films were fabricated by the sputter deposition technique at NTNU Nanolab and afterwards a FMR-experiment were performed on them at the temperatures 180K, 210K, 240K, 280K, 330K and 360K. The anisotropy field, exchange bias and offset field were extracted and analysed. The results revealed vastly higher magnitude of anisotropy field and exchange bias for the 4 Cr film, compared to the other samples. Under 300K, the anisotropy field of 4Cr is ~60 Oe which is about 30 times larger than anisotropy field of the other samples. The exchange bias for 4Cr is ~8 Oe, which is about 10 times larger than the exchange bias of the other samples. The significant difference in exchange bias is explained by the spin-density wave amplitude, which increases for decreasing Cr-thicknesses. However, this model does not predict the large drop-off to the 7 Cr, 10 Cr and 13 Cr samples. The measurement of PyCu revealed an exchange bias of the same order as the 7-13 Cr samples, indicating that the exchange coupling between the Py and Cr layer is very weak, since it is of the same magnitude as the PyCu film. A theoretical description of H_Res and Delta H of the system was given, but not fulfilled. Factors, mainly due to spin pumping and interface effects must be identified and adapted to the equations.
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Hussain, A. A. "Spin wave and ferromagnetic resonance studies on single crystal nickel films." Thesis, University of York, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354383.
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Gueye, Mouhamadou. "Magnetic thin films on flexible substrates : magnetomechanical study by ferromagnetic resonance." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCD007/document.
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Les films minces déposés sur des substrats flexibles ont été intensivement étudiés ces dernières années en raison de leur nombreuses applications en électronique flexible. Depuis peu, l'électronique flexible est étendu aux matériaux magnétiques conduisant ainsi au domaine émergeant de la magnéto-électronique flexible actuellement à l'avant garde des sujets de recherche de la spintronique. Ce travail de thèse est dédié à l'étude des propriétés magnéto-mécaniques de films minces magnétiques (Ni, NiFe, Co2FeAl, CoFeB, FeCuNbSi) sur des substrats flexibles. Les analyses structurales ont montré que les films de Ni et de CFA sont polycristallins non-texturés ; le CFB est amorphe. Par conséquent, les propriétés élastiques et magnéto-élastiques de ces films sont considérées comme étant isotropes. Une technique basée sur une utilisation conjointe d'essai mécanique, la résonance ferromagnétique (FMR) et la corrélation d'images numériques (CIN) a été développée pour étudier les propriétés magnéto-mécaniques de films minces sur substrats flexibles. A l'aide de cette méthode, il est possible de suivre l'évolution de l'anisotropie résiduelle omniprésente dans les films magnétiques sur substrats flexibles. Cette anisotropie est liée aux propriétés mécaniques contrastées lorsqu'on dépose un film mince rigide (grand module d'Young) sur un substrat flexible (petit module d'Young). L'effet du recuit sur les propriétés élastiques et magnéto-élastiques a été soigneusement étudié dans le film CFB validant ainsi l'intérêt porté à ses alliages pour des applications en spintronique. Enfin, la résonance ferromagnétique est employé en balayage en fréquence pour suivre la variation de la direction de l'aimantation en fonction des déformations induites par l'application de tension électrique sur l'actionneur piézoélectrique. Un retournement de 90° de la direction de l'aimantation dans le film Co2FeAl sur substrat flexible de Kapton® est observéThin films deposited on flexible substrates have been widely studied in the last decades due to the numerous applications in flexible electronics. Recently, flexible electronics have been extended to magnetic materials leading to the so-called emerging feld of flexible magnetoelectronics which is actually at the cutting-edge of spintronics research topics.This thesis is devoted to the study magnetomechanical properties of magnetic thin films (Ni, NiFe, Co2FeAl, CoFeB, FeCuNbSi) on flexible substrates. Structural analysis have 130 Abstracts hown that the Ni and CFA films are found to be polycrystalline with no strong preferred orientations ; the CFB film is amorphous. Consequently, the elastic and magnetoelastic properties are isotropic. For the study of the magnetomechanical properties, a set-up based on a jointly use of deformation test (bending or piezoactuation), ferromagnetic resonance (FMR) and digital image correlation (DIC) have been developped. Thanks to this method, it is possible to follow the evolution of the inescapable residual anisotropy encountered in magnetic thin films on flexible substrates under deformation and to determine the effective coefficient of magnetostriction of the films (sometimes unknown).This residual anisotropy is ascribed to contrasted mechanical strength when a sti thin film is deposited on a compliant substrate. The effect of the annealing temperature on the elastic and magnetoelastic have been studied carefully in CFB validating then theinterest on such alloys for spintronics applications. Finally, we have employed FMR inits sweep frequency mode to study the effective evolution of magnetization direction as function of the voltage-induced strains. A 90-degree magnetization rotation in Co2FeAl thin film on Kapton® polyimide substrate is observed
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Zhang, Zhenyong. "Ferromagnetic resonance study in exchange coupled magnetic/"non-magnetic" multilayer structures /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487856076413539.
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Bhat, Vinayak S. "A Study of Periodic and Aperiodic Ferromagnetic Antidot Lattices." UKnowledge, 2014. http://uknowledge.uky.edu/physastron_etds/25.
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This thesis reports our study of the effect of domain wall pinning by ferromagnetic (FM) metamaterials [1] in the form of periodic antidot lattices (ADL) on spin wave spectra in the reversible regime. This study was then extended to artificial quasicrystals in the form of Penrose P2 tilings (P2T). Our DC magnetization study of these metamaterials showed reproducible and temperature dependent knee anomalies in the hysteretic regime that are due to the isolated switching of the FM segments. Our dumbbell model analysis [2] of simulated magnetization maps indicates that FM switching in P2T is nonstochastic. We have also acquired the first direct, two-dimensional images of the magnetization of Permalloy films patterned into P2T using scanning electron microscopy with polarization analysis (SEMPA). Our SEMPA images demonstrate P2T behave as geometrically frustrated networks of narrow ferromagnetic film segments having near-uniform, bipolar (Ising-like) magnetization, similar to artificial spin ices (ASI). We find the unique aperiodic translational symmetry and diverse vertex coordination of multiply-connected P2T induce a more complex spin-ice behavior driven by exchange interactions in vertex domain walls, which differs markedly from the behavior of disconnected ASI governed only by dipolar interactions.
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Soares, Gabriel 1988. "Competição entre anisotropias perpendiculares em bicamadas de CoCrPt/Ni resolvida por ressonância ferromagnética." [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/276925.
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Orientadora: Fanny BéronDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Desde a descoberta dos filmes finos magnéticos com anisotropia perpendicular, ou PMAs (Perpendicular Magentic Anisotropy, em inglês), se tornou possível aumentar drasticamente a densidade de dados em discos rígidos. Uma maneira de continuar a incrementar a densidade final de dados seria desalinhar o eixo de anisotropia uniaxial e o campo magnético de escrita. Para isso, necessita-se de materiais com anisotropia magnética intermediária, i.e, na qual o seu eixo fácil está entre a longitudinal ao plano e a sua perpendicular. A situação ótima seria com o eixo fácil a 450, teoricamente dobrando a densidade final. No entanto, fabricar grãos ou filmes com esta propriedade não é viável do ponto de vista industrial. Todavia, bicamadas podem ser utilizadas para imitar este comportamento, onde um filme com anisotropia longitudinal é depositado sobre um PMA. Além do mais, esta abordagem apresenta a possibilidade de maior velocidade de escrita. Bicamadas de CoCrPt/Ni podem ser utilizadas para este propósito, com a camada de CoCrPt como PMA e a de Ni com anisotropia longitudinal. O experimento de ressonância ferromagnética permite, a priori, resolver as contribuições de anisotropia de cada camada no sistema de bicamadas, juntamente com os mecanismos de amortecimento magnético. O objetivo principal desta dissertação de mestrado é introduzir os conceitos de experimentação e teoria desta técnica, e aplicá-los nas bicamadas de CoCrPt/Ni. Neste trabalho foram utilizados filmes já depositados por sputtering com 10 nm de Co66Cr22Pt12, seguidos de 5 a 40 nm de Ni, para investigar o efeito da camada com anisotropia longitudinal sobre o PMA. Um outro conjunto de amostras contém um espaçador de Ti entre as camadas magnéticas, a fim de se estudar a interação na interface entre elas. Os experimentos de ressonância foram realizados em varredura de frequência num analisador de rede vetorial com campos magnéticos aplicados longitudinais ou perpendiculares e numa cavidade de banda X (9,54GHZ) em função da orientação do campo aplicado. Foi verificado qualitativamente o decréscimo da energia de anisotropia longitudinal com menores espessuras de Ni nas bicamadas. No entanto, não foi possível observar a linha de absorção da camada de CoCrPt, e consequentemente, encontrar unequivocamente as constantes de anisotropia do sistema, muito menos confirmar o comportamento multiaxial encontrado. Não obstante, foi confirmado a natureza de curto alcance da interação entre as camadas. Nova experimentação em outras bandas de frequência é necessária, afim de identificar a absorção do CoCrPt. Uma perspectiva futura interessante é o estudo da largura de linha e o amortecimento magnético do sistema devido a interação envolvida
Abstract: Since the advent of perpendicular magnetic anisotropy media, or PMAs, it was possible to greatly enhance the data density of hard drives. A method to push forward the data density increase is to misalign the anisotropy and applied field axes. This can be achieved by tilted media, i.e., in which the anisotropy axis lays somewhere between in-plane (IP) and out-of-plane (OOP). The optimal condition is with the axis tilted by 45\textsuperscript{0}. However, produce this kind of material is not practible at industrial scale. Thus, composite media can be used to mimic this behavior, where an in-plane anisotropy media is deposited on top of a PMA. Nonetheless, this approach allows to reach faster switching rates. CoCrPt/Ni bilayers may be used for this purpose, with the CoCrPt serving as the PMA and the Ni as the IP anisotropy layer. The ferromagnetic resonance experiment (FMR) can be used to obtain information about the magnetic anisotropy, being able to characterize its constant for each layer in the bilayer system, together with the damping mechanisms. Therefore, the main goal of this master thesis is to introduce the FMR theory and experimentation and apply them in this system. The used films were already deposited by sputtering with 10 nm of Co.66Cr.24Pt.12 under a 5 to 40 nm Ni layer. Another set of samples with a Ti layer between the magnetic layers provides information of the interface coupling. The FMR experiments were partly performed in a broadband vector network analyzer (VNA) with applied magnetic fields IP or OOP, and in a X-band (9,54 GHz) cavity as function of the orientation of the applied magnetic field. It was qualitatively verified a decrease of the longitudinal magnetic anisotropy energy as a function of the Ni thickness in the bilayer system. However, the CoCrPt single layer absorption could not be observed, making it impossible to unequivocally identify each anistropy constant. Nonetheless, the short-range nature of the coupling was confirmed. Further experimentation in higher frequencies is needed in order to find the CoCrPt absorption. Also, promising effects in the damping mechanism due to the coupling are expected
Mestrado
Física
Mestre em Física
2013/1186360
CAPES
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Adur, Rohan. "Magnetic Coupling and Relaxation at Interfaces Measured by Ferromagnetic Resonance Spectroscopy and Force Microscopy." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406120604.
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Lawson, Graham Richard. "Swept frequency absorption in particulate magnetic materials." Thesis, Manchester Metropolitan University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296486.
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Hiebert, Wayne Kevin. "Ferromagnetic resonance in a permalloy microstructure using time resolved scanning Kerr effect microscopy." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0006/MQ28942.pdf.
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Rodan, Steven. "Nuclear magnetic resonance and specific heat studies of half-metallic ferromagnetic Heusler compounds." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-198412.
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Half-metallic ferromagnets (HMFs), with fully spin-polarized conduction electrons, are prime candidates for optimizing spintronic devices. Many Heusler compounds (a class of ternary and quaternary intermetallics) are predicted to be HMFs, in particular Co$_{2}YZ$ (where $Y$ is usually another transition metal, and $Z$ is an s-p element). Crystal structure is controlled by thermodynamics to a large extent. Ideally, one should be able to control and optimize properties which are of interest by appropriately "tuning" the structure (e.g. annealing), but first one must understand the structure and its relation to observed physical properties. A local structural probe technique such as nuclear magnetic resonance (NMR) is an essential tool for identifying and quantifying the various atomic-scale orderings. Different Heusler structure types and antisite disorders affect the material's physical properties.
In this thesis, order-disorder phenomena in both bulk and thin film samples of Co$_2$Mn$_{1-x}$Si$_x$ and Co$_2$Mn$_{1-x}$Fe$_x$Si have been systematically studied using NMR. Though it is the films which are directly implemented in actual devices, studying bulk samples as model systems provides invaluable information regarding the material properties.
The evolution of local atomic structure in numerous thin films has been shown to depend greatly on preparation parameters, including post-deposition annealing temperature, and specific stoichiometry. For Co$_2$MnSi films, the ideal post-annealing temperature for promoting the $L2_1$ atomic structure was found; the threshold temperature above which structure continues to become higher-ordered in the bulk, but where too much interdiffusion at the buffer interface occurs, degrading the smooth interfaces necessary for high magnetoresistance ratios. NMR also adds evidence that Co$_2$Mn$_x$Si$_{0.88}$ ($x>$1) electrodes in magnetic tunnel junctions have highest tunneling magneto-resistance because the excess Mn suppresses the formation of detrimental Co$_{Mn}$ antisites.
A systematic investigation of several thermal and magnetic properties, including Sommerfeld coefficients, Debye temperatures, saturation magnetic moments, spin-wave stiffness, and magnon specific heat coefficient, were measured for selected Co$_2$-based ternary and quaternary Heusler compounds. Obtained values were compared with theoretical ones calculated using electronic band structure methods. It has been systematically shown that adding a magnon term to the specific heat has a negligible effect on the electronic contribution in all cases.
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Ogrin, Feoder. "Ferromagnetic resonance studies of cobalt films and cobalt based multilayers produced by MOCVD." Thesis, Keele University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362165.
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Liutyi, Taras Volodymyrovych, Тарас Володимирович Лютий, Тарас Владимирович Лютый, and O. M. Hryshko. "Magnetic and Mechanical Resonance of a Single Ferromagnetic Nanoparticle in a Viscous Fluid." Thesis, Sumy State University, 2017. http://essuir.sumdu.edu.ua/handle/123456789/64155.
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Resonance is a widely spread phenomenon in our life. The mathematical apparatus for this phenomenon was developed absolutely, and a lot of examples, both desirable and undesirable were studied in detail. Thus, in particular, the resonance behavior of the nanoparticle magnetic moment driven by an external alternating field was scrutinized in. Here the nanoparticle was considered to be embedded into a solid matrix.
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Karube, Kosuke. "Ferromagnetic critical behavior and critical universality in itinerant-electron metamagnet UCoAl." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199086.
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Hattori, Taisuke. "Spin-Triplet Superconductivity Induced by Ferromagnetic Fluctuations in UCoGe." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188471.
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Johansson, August. "Interlayer exchange coupling in Co/Pd-NiFe films studied by Vector Network Analyser Ferromagnetic Resonance." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/interlayer-exchange-coupling-in-copdnife-films-studied-by-vector-network-analyser-ferromagnetic-resonance(cdb5170e-aa10-43ef-86c7-f61cf8a187f9).html.
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A greater understanding of precessional dynamics in magnetic systems is central to several emerging technologies. This thesis presents the design, construction and development of a Vector Network Analyser based Ferromagnetic Resonance measurement instrument (VNA-FMR), and its application in characterising dynamic material properties in hybrid anisotropy [CoPd]8-NiFe films, produced by remote plasma sputtering. Potential applications for hybrid films include Spin Torque Oscillators (STOs) or Vortex Oscillators (VO) for use as microwave emitters in, for example in Microwave Assisted Magnetic Recording (MAMR). The VNA-FMR system was first used to measure thin films of NiFe (permalloy) which allowed its capabilities to be quantified and compared to systems reported in the literature. The instrument demonstrated the capability of measuring permalloy films down to a thickness of 3 nm and was used to measure resonance and damping behaviour which agreed well with theory. The results obtained forMs were in agreement with measurement using Vibrating Sample Magnetometry. The effect of interlayer exchange on FMR was explored in hybrid films using a sample series with varying Pd spacer layer thickness, t, [Co/Pd]-Pd(t)-NiFe. As Pd spacer thickness increased, a transition was observed from near complete coupling with a single resonance mode to separate acoustic and optical branches of resonance. As spacing was further increased, the branches converged towards the resonances of the individual component layers of the hybrid films. The results suggest exchange coupling has a range of less than 2 nm, and is completely extinguished at 5 nm, in agreement with previous measurements. However, a change in damping behaviour was observed between 10 and 20 nm spacer thickness, independent of field orientation.
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Trindade, Gonçalves Francisco José. "Engineering of demagnetisation fields in exchange biased antidots studied using ferromagnetic resonance and Lorentz microscopy." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6875/.
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Nanostructured ferromagnetic materials have gained considerable attention recently for use in novel devices in the areas of data storage, microwave signal processing and propagation of electromagnetic waves. Structural modifications allow a control over the internal magnetic properties of the system down to the nanoscale. Lateral confinement gives rise to a distribution of demagnetisation fields in the plane of the thin film which can create interesting effects on static and dynamic magnetic properties. In the context of this dissertation, nanostructuring is used as a means to engineer the static and dynamic response of magnetic systems. In particular, periodic arrays of holes embedded in continuous films are studied. With patterning one observes the emergence of an anisotropic field dependence as well as the emergence of non-uniform spin precession modes due to the dipole distribution at the film interfaces. These properties were probed primarily using a technique called broadband ferromagnetic resonance, whereby a microwave field drives the local spin dynamics of the magnetic system. A way to further modify the magnetic properties induced due to the symmetry of the periodic structuring is by introducing an unidirectional field contribution which is characteristic of an exchange biased system. It was found that the magnetic pole distribution in antidots is particularly sensitive to the effects of exchange bias, giving rise to an asymmetric frequency response with respect to the applied field. The asymmetric microwave properties of an exchange biased FeMn/NiFe system with antidot structuring, obtained using electron beam lithography, are investigated. The ferromagnetic resonance (FMR) spectra exhibited several magnetostatic spin wave modes with 8-fold and 4-fold anisotropy components. Moreover, it was observed that large frequency asymmetries are obtained along the directions 10 degrees off the main antidot lattice axes, as result of the competing anisotropies. Brillouin light scattering measurements showed the presence of a magnonic band gap as expected for this type of structure. To interpret these observations, the spin precessional modes obtained experimentally are correlated with localised mode profiles obtained by micromagnetic simulations. This hybrid structure is a good candidate for applications such as selective microwave filtering and for use in multi-state magnetic logic. The prospects of using patterned exchange biased systems to engineer microwave properties is greatly increased if one goes beyond the 2-dimensional perspective. In multilayered structures, one can modify the magnetic properties layer-by-layer to achieve the desired response. This concept is demonstrated here by using a three dimensional structure in which an exchange biased and a free magnetic layer are stacked upon one another and patterned with an antidot configuration. The exchange bias acts as a pinning field for one layer, while the free layer reverses, promoting a zero net moment state. Interlayer dipole interactions are found to result in the partial cancellation of the microwave response. Micromagnetic simulations support the existence of a diminished microwave response which was confirmed by FMR measurements of an equivalent structure. The net moment cancellation, indicative of the antiparallel alignment, was observed on a Lorentz differential phase contrast scanning transmission electron microscope equipped with an FMR probe, which was designed and built for the purpose. This unique tool allows access to complex microwave response while the ground state of a nanostructured film is imaged via Lorentz microscopy. From the magnetostatic viewpoint, our results differ greatly from previous studies in a way that this sample shows distinct magnetic history and the near remanence states exhibit unique magnetic textures: magnetic vortices. The applicability of the TEM in-situ FMR probe was extended to the mapping of radio frequency electromagnetic (EM) fields using low angle diffraction (LAD) imaging. The electron beam, propagating in a sample free environment, experiences the field distribution generated by the microstrip waveguide, which alters the electron amplitude and phase, as described by the Aharonov-Bohm effect, and results in different intensity profiles at the detector. As the microwave frequencies were varied, the different polarisation states are imaged directly. Microwave simulations allowed the EM field distribution to be calculated, which was used to reproduce the LAD results. A knowledge of the near field distribution in antennas is often a challenging task so this technique opens up new opportunities for planar devices operating in high vacuum conditions.
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Back, Markus. "Out-of-plane Ferromagnetic Resonance (FMR) measurements on magnetic nanoparticle dispersions for biomedical sensor applications." Thesis, Uppsala universitet, Fasta tillståndets fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-410179.
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In this master work, we investigated the feasibility of a magnetic resonance measurement technique using magnetic nanoparticle dispersions in both liquid and solid form. The implementation is realised as a coplanar waveguide operating in the frequency range of 0.5 - 20 GHz and an electromagnet producing a static magnetic field of strength up to 1.2 T. The Gilbert magnetic damping factor is determined for polymer composites of magnetic nanoparticles and the gyromagnetic ratio is determined for both nanoparticle dispersions in liquid form and polymer composites.
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Wei, Yajun. "Ferromagnetic Resonance as a Probe of Magnetization Dynamics : A Study of FeCo Thin Films and Trilayers." Doctoral thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-247238.
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The high frequency dynamic magnetic responses of FeCo thin films and structures have been investigated mainly using ferromagnetic resonance (FMR) technique. The FMR resonance condition and linewidth are first derived from the dynamic Landau- Lifshitz-Gilbert equation, followed by a study of the conversion between FMR field and frequency linewidths. It is found that the linewidth conversion relation based on the derivative of resonance condition is only valid for samples with negligible extrinsic linewidth contribution. The dynamic magnetic properties obtained by using FMR measurements of FeCo thin films grown on Si/SiO2 substrates with varying deposition temperatures is then presented. The effective Landé g-factor, extrinsic linewidth, and Gilbert relaxation rate are all found to decrease in magnitude with increasing sample growth temperature from 20oC to about 400–500oC and then on further increase of the growth temperature to increase in magnitude. Samples grown at about 400–450oC display the smallest coercivity, while the smallest value of the Gilbert relaxation rate of about 0.1 GHz is obtained for samples grown at 450–500oC. An almost linear relation between extrinsic linewidth and coercivity is observed, which suggests a positive correlation between magnetic inhomogeneity, coercivity and extrinsic linewidth. Another major discovery in this study is that the Gilbert relaxation decreases with increasing lattice constant, which is ascribed to the degree of structural order in the films. A micromagnetic model is established for an asymmetric trilayer system consisting of two different ferromagnetic (FM) layers separated by thin non-magnetic (NM) layer, treating the magnetization in each FM layer as a macrospin. Based on the model, numerical simulations of magnetization curves and FMR dispersion relations, of both the acoustic mode where magentizations in the two FM layers precess in phase and the optic mode where they precess out-of-phase, have been carried out. The most significant implication from the results is that the coupling strength can be extracted by detecting only the acoustic mode resonances at many different unsaturated magnetic states using broadband FMR technique. Finally, trilayer films of FeCo(100 Å)/NM/FeNi(100 Å) with NM=Ru or Cu were prepared and studied. The thickness of the Ru and Cu spacer was varied from 0 to 50 Å. For the Ru spacer series, the film with 10 Å Ru spacer shows antiferromagnetic coupling while all other films are ferromagnetically coupled. For the Cu spacer trilayers, it is found that all films are ferromagnetically coupled and that films with thin Cu spacer are surprisingly strongly coupled (the coupling constant is 3 erg/cm2 for the sample with 5 Å Cu spacer). The strong coupling strength is qualitatively understood within the framework of a combined effect of Ruderman-Kittel- Kasuya-Yosida interaction and pinhole coupling, which is evidenced by transmission electron microscopy analysis. The magnetic coupling constant decreases exponentially with increasing Cu spacer thickness, without showing an oscillatory thickness dependence. The results have implications for the design of multilayers for spintronic applications.
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Elster, Lars. "Magnetic resonance in superconducting junctions." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY042/document.
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Dans cette thèse, on analyse la possibilité de changer un courant de charge dans des jonctions supraconductrices par une manipulation des propriétés de spin en utilisant la résonance magnétique. On considère deux jonctions différentes: Premièrement, une jonction Josephson non-conventionnelle entre un supraconducteur conventionel de type s et un supraconducteur non-conventionel de type px. Deuxièmement, une jonction entre un demi-métal et un supraconducteur conventionel. La jonction spx contient deux états liés d'Andreev qui sont 2pi-periodiques. Ils donnent lieu à une aimentation spontanée à l'équilibre. Ceci ouvre la possibilité de manipuler l'occupation des niveaux d'Andreev en utilisant un champ magnétique dépendant du temps. On demontre que ce champ induit des oscillations de Rabi cohérentes entre différents états de spin de la jonction. Ces oscillations se manifestent comme des résonances dans la relation courant-phase de la jonction. Pour un champ polarisé circulairement, on trouve une règle de sélection de spin qui autorise des oscillations de Rabi seulement dans un certain interval de phases dans la relation courant-phase permettant une éventuelle détection du spin. De plus, le champ induit des transitions non-cohérentes qui nécessitent la présence d'une quasiparticule dans le continuum d'états. Ces transitions agissent comme processus de recharge et d'ionization pour les niveaux d'Andreev. Pour un champ polarisé circulairement, ces processus induits par le champ ne donnent pas lieu à un mécanisme de relaxation pour les oscillations de Rabi à cause des contraintes en spin et en énergie. Pour un champ polarisé linéairement, il n'y a pas de règle de selection de spin et la largeur des résonances de Rabi dans la relation courant-phase est déterminée par les processus d'ionization induits par le champs. Dans la jonction entre le demi-métal et le supraconducteur conventionel, il n'y a pas de courant pour une aimentation statique, puisque la polarization parfaite en spin du demi-métal interdit les processus de réflexion d'Andreev à l'interface. On demontre que pour une géométrie de point contact, un courant d'Andreev passe, si le demi-métal est soumis à la résonance ferromagnétique. La précession de la direction de l'aimentation dans le demi-métal donne lieu au mécanisme de spin-flip nécessaire. Le courant est forcé par la précession de la direction de l'aimentation qui crée une situation hors équilibre pour les porteurs de charge. De plus, dans un matériau ferromagnétique avec une densité de porteurs minoritaires non-nulle, le courant est réduit et disparaît si les densités majoritaires et minoritaires sont égales. On considère, par ailleurs, une géométrie d'interface étendue, plus réaliste. Pour une jonction ballistique, le courant est augmenté par rapport à la géometrie de point contact, en raison du nombre plus élevé de canaux. De plus, on demontre que le désordre est le plus important dans le matériau ferromagnétique. Le courant d'Andreev à travers la jonction désordonnée est beaucoup plus grand que le courant à travers la jonction ballistique dans la même géométrieIn this thesis we investigate the possibility to change the charge current in superconducting junctions by manipulating the spin properties using magnetic resonance. We consider two different junctions: First, an unconventional Josephson junction between a conventional s-wave superconductor and an unconventional px-wave superconductor and second a half-metal/conventional superconductor junction. The spx junctions hosts two spin-polarized Andreev bound states, which are 2pi-periodic, giving rise to a spontaneous magnetization in equilibrium. This opens the possibility to manipulate the occupations of the Andreev levels using a time-dependent magnetic field. We show that the field induces coherent Rabi oscillations between different spin states of the junction that appear as resonances in the current-phase relation. For a cicularly polarized magnetic field, we find a spin selection rule, giving Rabi oscillations only in a certain range of superconducting phase differences, which provides a spin detection scheme. In contrary, for a linear polarization, there is no spin constraint on the Rabi oscillations. The field also induces non-coherent transitions including continuum states that act as refill and ionization processes for the Andreev levels. For a circularly polarized field, these field-induced processes do not provide a decay mechanism for Rabi oscillations, due to spin and energy constraints. For a linear polarization, the width of the Rabi resonances in the current-phase relation is determined by the field-induced ionization processes. In the half-metal/conventional superconductor junction no Andreev current may flow for a static magnetization direction, since the perfect spin polarization of the half-metal forbids Andreev reflection processes at the interface. We show that an Andreev current flows, if the half-metal is subject to ferromagnetic resonance. The precessing magnetization direction in the half-metal provides the necessary spin-flip mechanism. The current is driven by the precession of the magnetization direction that creates a non-equilibrium situation for the charge carriers. We also show for a point contact geometry that in a ferromagnet with non-zero minority carrier concentration the current is reduced and vanishes at equal minority and majority carrier concentrations. Additionally, we consider a more realistic, extended interface geometry. For a ballistic junction, the current is enhanced compared to a point contact geometry due to the larger number of transport channels. Furthermore, we show that disorder is most important in the ferromagnet. The Andreev current through the disordered junction is much larger than the current through a ballistic junction in the same geometry
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Wittmann, Angela Dorothea Anshi. "Spin currents in organic semiconductors." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/290148.
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Organic semiconductors have recently been found to have a comparably large spin diffusion time and length. This makes them ideal candidates for spintronic devices. However, spin injection, transport and detection properties in organic materials have yet to be fully understood. This work studies spin injection from ferromagnets into organic semiconductors via spin pumping. Furthermore, work towards thermal spin injection, and detection is presented and discussed. The first part of this thesis comprises the spin pumping experiments. Measuring linewidth broadening of the microwave absorption at ferromagnetic resonance due to increase in effective Gilbert damping by spin pumping from a ferromagnetic substrate into an adjacent non-magnetic semiconductor allows us to quantify the spin-mixing conductance. This technique is employed to demonstrate spin injection from a ferromagnetic metal, permalloy (Ni81Fe19), into organic small molecules and conjugated polymers as well as to quantify the spin injection efficiency. The results highlight the importance of structural properties of organic semiconductors at the interface to permalloy. Significant suppression of spin injection due to alkyl side-chains separating the core of the small molecules from the interface is exemplary for this finding. Furthermore, the spin-mixing conductance depends very sensitively on the charge carrier density within a certain range of doping level. This suggests a strong link between spin injection efficiency and spin concentration in the organic semiconductor at the interface to permalloy. The second part of the thesis aims to explore spin caloritronic effects. We study spin injection into organic semiconductors by probing the spin Seebeck effect by making use of the inverse spin Hall effect for spin-to-charge conversion. Moreover, we present experimental work towards observation of a novel effect, the inverse spin Nernst effect, for thermal spin detection.
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Kaster, Brian C. "Magnetic Properties of Co1-xFexS2." Miami University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=miami1311874514.
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Khanal, Shankar. "Study of Static and Dynamic Properties of Magnetic Nanostructures." ScholarWorks@UNO, 2017. http://scholarworks.uno.edu/td/2382.
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Magnetic materials are one of the most interesting and promising class of materials for technological applications [1]. Among them, patterned ferromagnetic systems have an important role especially in the prospect of high density data storage [2], domain wall logic devices [3] and magnetic memory [4, 5]. Coupled systems of ferromagnetic and antiferromagnetic materials have been implemented to design sensors such as giant magnetoresistance (GMR) [6-8] and tunnel magnetoresistance (TMR) [9, 10]. Ferromagnetic nanoparticles have been used for the drug targeting, cancer therapy, MRI and many more applications [11, 12]. In addition, more recently, significant attention has been paid to explore the dynamic properties of magnetic materials in the GHz range and use them for technological applications such as microwave filters, signal processing, phase shifter, nonreciprocal microwave devices, spin wave guide, high frequency memory, logic elements [13-19]
Boundary conditions, interactions between individual entities, and lateral confinement of magnetic charges generate diverse magnetic properties especially at nanoscale length [20, 21]. The variation of magnetic properties are even quite different when the size of the magnetic structure is smaller or comparable with the magnetic characteristic length such as mean free path of electron, width of domain wall and even the spin diffusion length [22-24].
In this study, we have considered different magnetic systems. Firstly, the multilayer of coupled ferromagnetic and antiferromagnetic system has been considered to evaluate the exchange bias anisotropy. [FeNi/IrMn]n multilayer systems with different thicknesses of ferromagnetic layer were studied. Static and dynamic properties were revealed through magnetometry measurements (VSM) and VNA-FMR techniques respectively. Angular variation of first order reversal curve (AFORC) and ferromagnetic resonance (AFMR) were performed to learn the intrinsic exchange bias distribution. Secondly, patterned magnetic structures were synthesized to understand the magnetization dynamics in confined geometry. Surface modulated thin films with different periodicity, dumbbell-shaped structures with variable size and three dimensional magnonic crystals have been studied using both static and dynamic measurement techniques. Micromagnetic simulations were performed to understand and explain the experimental results.
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Manago, Masahiro. "Enhancement of Spin-Triplet Superconductivity by Pressure-Induced Critical Ferromagnetic Fluctuations in UCoGe." Kyoto University, 2019. http://hdl.handle.net/2433/242592.
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Markó, Daniel. "Magnetostatics and Dynamics of Ion Irradiated NiFe/Ta Multilayer Films Studied by Vector Network Analyzer Ferromagnetic Resonance." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-64289.
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In the present work, the implications of ion irradiation on the magnetostatic and dynamic properties of soft magnetic Py/Ta (Py = Permalloy: Ni80Fe20) single and multilayer films have been investigated with the main objective of finding a way to determine their saturation magnetization. Both polar magneto-optical Kerr effect (MOKE) and vector network analyzer ferromagnetic resonance (VNA-FMR) measurements have proven to be suitable methods to determine µ0MS, circumventing the problem of the unknown effective magnetic volume that causes conventional techniques such as SQUID or VSM to fail. Provided there is no perpendicular anisotropy contribution in the samples, the saturation magnetization can be determined even in the case of strong interfacial mixing due to an inherently high number of Py/Ta interfaces and/or ion irradiation with high fluences. Another integral part of this work has been to construct a VNA-FMR spectrometer capable of performing both azimuthal and polar angle-dependent measurements using a magnet strong enough to saturate samples containing iron. Starting from scratch, this comprised numerous steps such as developing a suitable coplanar waveguide design, and writing the control, evaluation, and fitting software. With both increasing ion fluence and number of Py/Ta interfaces, a decrease of saturation magnetization has been observed. In the case of the 10×Py samples, an immediate decrease of µ0MS already sets in at small ion fluences. However, for the 1×Py and 5×Py samples, the saturation magnetization remains constant up to a certain ion fluence, but then starts to rapidly decrease. Ne ion irradiation causes a mixing and broadening of the interfaces. Thus, the Py/Ta stacks undergo a transition from being polycrystalline to amorphous at a critical fluence depending on the number of interfaces. The saturation magnetization is found to vanish at a Ta concentration of about 10–15 at.% in the Py layers. The samples possess a small uniaxial anisotropy, which remains virtually unaffected by the ion fluence, but slightly reduces with an increasing number of Py/Ta interfaces. In addition to magnetostatics, the dynamic properties of the samples have been investigated as well. The Gilbert damping parameter α increases with both increasing number of Py/Ta interfaces and higher ion fluences, with the former having a stronger influence. The inhomogeneous linewidth broadening ΔB0 increases as well with increasing number of Py/Ta interfaces, but slightly decreases for higher ion fluencesIn dieser Dissertation ist der Einfluss von Ionenbestrahlung auf die magnetostatischen und dynamischen Eigenschaften von weichmagnetischen Py/Ta-Einzel- und Multilagen (Py = Permalloy: Ni80Fe20) untersucht worden, wobei das Hauptziel gewesen ist, eine Methode zur Bestimmung der Sättigungsmagnetisierung zu finden. Sowohl polare magneto-optische Kerr-Effektmessungen (MOKE) als auch ferromagnetische Resonanzmessungen mittels eines Vektornetzwerkanalysators (VNA-FMR) haben sich als geeignet erwiesen, um µ0MS zu bestimmen, wobei das Problem des unbekannten effektiven magnetischen Volumens umgangen wird, welches bei der Verwendung von Techniken wie SQUID oder VSM auftreten würde. Unter der Voraussetzung, dass die Proben keinen senkrechten magnetischen Anisotropiebeitrag besitzen, kann die Sättigungsmagnetisierung selbst im Fall starker Grenzflächendurchmischung infolge einer großen Anzahl an Py/Ta-Grenzflächen und/oder Ionenbestrahlung mit hohen Fluenzen bestimmt werden. Ein weiterer wesentlicher Bestandteil dieser Arbeit ist die Konstruktion eines VNA-FMR-Spektrometers gewesen, welches vollautomatisiert ist, polare und azimutale Winkelabhängigkeiten messen kann und einen Magneten besitzt, der Proben, die Eisen beinhalten, sättigen kann. Von Grund auf beginnend umfasste dies zahlreiche Schritte wie z. B. die Entwicklung eines geeigneten koplanaren Wellenleiterdesigns sowie das Schreiben von Steuerungs-, Auswertungs- und Fitprogrammen. Mit steigender Fluenz und Zahl an Py/Ta-Grenzflächen ist eine Abnahme der Sättigungsmagnetisierung beobachtet worden. Im Fall der 10×Py-Proben findet diese bereits bei kleinen Fluenzen statt. Im Gegensatz dazu bleibt µ0MS der 1×Py- und 5×Py-Proben bis zu einer bestimmten Fluenz konstant, bevor sie sich dann umso schneller verringert. Die Bestrahlung mit Ne-Ionen verursacht eine Durchmischung und Verbreiterung der Grenzflächen. Infolgedessen erfahren die Py/Ta-Proben bei einer kritischen Fluenz, die von der Zahl der Grenzflächen abhängig ist, einen Phasenübergang von polykristallin zu amorph. Die Sättigungsmagnetisierung verschwindet ab einer Ta-Konzentration von etwa 10–15 Atom-% in den Py-Schichten. Die Proben besitzen eine kleine uniaxiale Anisotropie, die praktisch unbeeinflusst von der Fluenz ist, sich jedoch mit steigender Zahl an Py/Ta-Grenzflächen leicht verringert. Neben den statischen sind auch die dynamischen magnetischen Eigenschaften der Proben untersucht worden. Der Gilbert-Dämpfungsparameter α erhöht sich sowohl mit steigender Zahl an Py/Ta-Grenzflächen als auch mit höheren Fluenzen, wobei Erstere einen größeren Einfluss hat. Die inhomogene Linienverbreiterung ΔB0 nimmt ebenfalls mit steigender Zahl an Py/Ta-Grenzflächen zu, verringert sich jedoch bei größeren Fluenzen leicht
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Ruane, William Terrence. "Controllable Spin Wave Generation with Spatially Dependent Magnetic Fields and Their Detection Using Ferromagnetic Resonance Force Microscopy." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524171463673634.
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Bechtel, Kyle A. "MAGNETIC RESONANCE IN THE PROXIMITY OF AN INSTABILITY: PERPENDICULAR RESONANCE IN PERMALLOY NEAR THE CRITICAL FIELD." Oxford, Ohio : Miami University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1250281122.
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Ciuciulkaite, Agne. "Micromagnetic simulations for the investigation of magnetic vortex array dynamics." Thesis, Uppsala universitet, Materialfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-280767.
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In this work the dynamics of permalloy circular magnetic islands of 225 nm radius and 10 nm thickness arranged into square lattices was investigated employing micromagnetic simulations.The simulations of the vortex magnetization loops and the ferromagnetic resonance (FMR) spectra were carried out using a free micromagnetics simulation software Mumax3. The obtained data was analyzed using Matlab. The simulations were carried out on a single vortex island as well as on two different lattices. The first lattice is comprised of interacting islands, while the second lattice - of non-interacting islands, separated by 25 nm and by 450 nm edge-to-edge distance, respectively. The magnetization loops were simulated by applying the static magnetic field in-plane of the single island or the lattice. The FMR simulations were carried out by applying the static magnetic field in-plane of the lattice and after the system reached the ground state in that field, the excitation as a sinc pulse was sent out along the out-of-plane direction of the lattice. The analysis of the obtained FMR spectra revealed that the several resonant modes are present for the single vortex island and the lattice, comprised of such islands. However, the physical explanation of the origin of those modes is a subject for further investigations.