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1
Tang, Huang, Deshuai Yang, Mengfei Lu, Shaoxi Kong, Yanghui Hou, Duanduan Liu, Depei Liu, et al. "Spin unlocking oxygen evolution reaction on antiperovskite nitrides." Journal of Materials Chemistry A 9, no. 45 (2021): 25435–44. http://dx.doi.org/10.1039/d1ta07561f.
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The spin state change of Fe3+ ions induced the paramagnetic Fe0.5Ni0.5OOH shell on the ferromagnetic Cu0.5NFe3Ni0.5 core via superexchange interaction, facilitating charge transfer and oxygen species ad(de)sorption for boosted OER performance.
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Das, Kalipada, R. Rawat, B. Satpati, and I. Das. "Giant enhancement of magnetoresistance in core-shell ferromagnetic-charge ordered nanostructures." Applied Physics Letters 103, no. 20 (November 11, 2013): 202406. http://dx.doi.org/10.1063/1.4830376.
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Das, Kalipada, and I. Das. "Magnetocaloric effect study of ferromagnetic-charge ordered core-shell type manganite nanostructures." Journal of Magnetism and Magnetic Materials 436 (August 2017): 97–100. http://dx.doi.org/10.1016/j.jmmm.2017.04.037.
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Levshin, G. E. "Magnetization of ferromagnetic charge at induction heating." Izvestiya. Ferrous Metallurgy 65, no. 2 (March 16, 2022): 85–91. http://dx.doi.org/10.17073/0368-0797-2022-2-85-91.
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The article presents analysis of magnetization and heating of ferromagnetic charge in crucibles of induction furnaces of two types. In inductor furnaces, the charge is magnetized by a vertical electromagnetic flow, and in electromagnetic furnaces with a curved U-, C-, or O-shaped magnetic circuit (MPr) – by a horizontal flow. Knowledge of these largely general magnetization processes is insufficient. Bi magnetic induction in charge material is rather important. There are difficulties in determining this parameter during magnetization of a single piece of charge and other magnetic quantities associated with it: Bm induction and Nm strength of the demagnetizing field, N demagnetization coefficient, M magnetization, magnetic permeabilities of μi substance and μt body, km susceptibility, etc. Difficulties increase at magnetization, if it is a porous body with crucible volume of ~V t and a factor of filling with ferromagnetic pieces of this volume of Kv ≤ 0.5. It also creates a demagnetizing field with Bmt induction and Hmt strength. Beyond that, pores have an additional demagnetizing effect. Therefore, the induction Вiт in a porous body is less than the induction Вi in a solid one. To compare magnetization of ferromagnetic charge with horizontal and vertical flows with frequency of 50 Hz, modeling experiments were carried out with the samples of DSL08 unconsolidated shot from high-carbon steel (GOST 11964 – 83) with Kv ≈ 0.53. The samples were placed in the inductor and between the poles of a U-shaped core piece. Induction was measured by a cylindrical and flat probe unit of Sh1-15 militeslameter in air and in the sample. An advantage of electromagnetic furnace over an inductor one is more uniform distribution of Bi induction in charge and its significant excess (1.7 times) over the Be induction in a furnace working cavity, which indicates more efficient use of electromagnetic energy in this furnace during heating. The author proposed to control Вi induction when heating the charge by the ammeter-voltmeter method using measuring coil made of heat-resistant wire.
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Lien, Le Thi Hong, Vu Ngoc Tuoc, Nguyen Viet Minh, and Tran Doan Huan. "A First Principles Study on Electronic and Magnetic Properties of Defects in ZnO/GaN Core-shell Nanowire Heterostructures." Communications in Physics 24, no. 3S1 (November 13, 2014): 127–35. http://dx.doi.org/10.15625/0868-3166/24/3s1/5463.
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To date semiconductor nanowire (NW) heterostructures (HS) have attracted extensive attention as important components of electronic and optoelectronic nanodevices. Further NWs also show promising potency to enhance the solar energy harvesting, e.g. improving both light trapping, photo-carrier collection, and contacting surface area. In this work we show theoretically that the \(d^{0}\)-ferromagnetism and NW HS bandgap can be turned by engineering the HS interfaces in non-magnetic ZnO/GaN core/shell NW HS. In that NW HS the incorporation of one compound into the other leads to the bandgap narrowing in the nonisovalent alloy because of the type II band alignment betwwen ZnO and GaN. The \(d^{0}\)-ferromagnetic interface can be developed by creating \(p\)-type defect with \(N\) and/or \(n\)-type defect with Zn in Ga--O interface bonds due to the defect-induced polar discontinuity. It's noted that the GaN/ZnO NW HS itself without defect or with same number defects of both types are not ferromagnetic. So that the induced magnetic moment is suggested to be related to the missing charge introduced at these defects. In our study we focused on the effects of GaN/ZnO interfaces on the electronic and magnetic properties, e.g. interface states within the bandgap and interface-induced ferromagnetism and impact of surface reconstruction and quantum confinement. The origin of this \(d^{0}\)-FM is revealed by analyses of spin-polarized bandstructure indicated by the asymmetrical spin-up and spin-down states near the Fermi level, the projected densities of states (PDOSs) and the spin-polarized mulliken charge differences, indicated that most spin-polarized states are dominated by the interface defect site N$p$ electrons. The calculated GaN/ZnO interface magnetism, have been compared with FM at the LaAlO\(-SrTiO\(_{3}\) interface which are theoretically predicted [30] and experimentally confirmed [31], where the magnetic moments also arise from the polar discontinuity.
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Das, Kalipada. "Investigation of magnetic and magneto-transport properties of ferromagnetic-charge ordered core-shell nanostructures." Journal of Applied Physics 122, no. 13 (October 7, 2017): 134301. http://dx.doi.org/10.1063/1.4993095.
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Li, Wei, Mahboobeh Shahbazi, Kaijian Xing, Tuquabo Tesfamichael, Nunzio Motta, and Dong-Chen Qi. "Highly Sensitive NO2 Gas Sensors Based on MoS2@MoO3 Magnetic Heterostructure." Nanomaterials 12, no. 8 (April 11, 2022): 1303. http://dx.doi.org/10.3390/nano12081303.
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Recently, two-dimensional (2D) materials and their heterostructures have attracted considerable attention in gas sensing applications. In this work, we synthesized 2D MoS2@MoO3 heterostructures through post-sulfurization of α-MoO3 nanoribbons grown via vapor phase transport (VPT) and demonstrated highly sensitive NO2 gas sensors based on the hybrid heterostructures. The morphological, structural, and compositional properties of the MoS2@MoO3 hybrids were studied by a combination of advanced characterization techniques revealing a core-shell structure with the coexistence of 2H-MoS2 multilayers and intermediate molybdenum oxysulfides on the surface of α-MoO3. The MoS2@MoO3 hybrids also exhibit room-temperature ferromagnetism, revealed by vibrating sample magnetometry (VSM), as a result of the sulfurization process. The MoS2@MoO3 gas sensors display a p-type-like response towards NO2 with a detection limit of 0.15 ppm at a working temperature of 125 °C, as well as superb selectivity and reversibility. This p-type-like sensing behavior is attributed to the heterointerface of MoS2-MoO3 where interfacial charge transfer leads to a p-type inversion layer in MoS2, and is enhanced by magnetic dipole interactions between the paramagnetic NO2 and the ferromagnetic sensing layer. Our study demonstrates the promising application of 2D molybdenum hybrid compounds in gas sensing applications with a unique combination of electronic and magnetic properties.
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Zou, Liang-Jian, and H. Q. Lin. "Phase Separation and Phase Diagram in Lightly Doped Manganites: Temperature and Magnetic Field Effects." Australian Journal of Physics 52, no. 2 (1999): 247. http://dx.doi.org/10.1071/p98057.
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The effects of magnetic field and temperature on the phase separation and phase diagram of lightly doped manganites are studied. Based on the double exchange model with on-site Coulomb interaction, we show that in the case of a homogeneous charge distribution, the canting angle of localised core spins and the critical doping concentration of the system from canted phase to ferromagnetic (FM) phase become large because the effective FM coupling between localised core spins is weakened when the temperature increases. The boundary of the canted phase and FM phase shifts to a high doping concentration regime at high temperatures. In comparison with with the zero-temperature result, the phase separation can take place more easily in lightly doped manganites at finite temperatures. The application of a magnetic field decreases the energy of the FM cluster in the system, favours the separation of the hole-rich FM phase from the antiferromagnetic (AFM) background, and shifts the cant-FM border to the low doping regime. The effect of the Jahn-Teller electron-phonon coupling on the phase diagram and phase separation is also discussed.
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Hossain, M. D., S. Dey, R. A. Mayanovic, and M. Benamara. "Structural and Magnetic Properties of Well-Ordered Inverted Core-Shell α-Cr2O3/ α-MxCr2-xO3 (M=Co, Ni, Mn, Fe) Nanoparticles." MRS Advances 1, no. 34 (2016): 2387–92. http://dx.doi.org/10.1557/adv.2016.324.
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ABSTRACTMagnetic core shell nanoparticles (NPs) have potential for applications in magnetic random access memory, spintronic devices, and drug delivery systems. Our investigations are focused on the synthesis of inverted core shell nanoparticles and characterization of their structural and magnetic properties. By using our hydrothermal nanophase epitaxy technique, we are able to synthesize well-ordered α-Cr2O3@α-MxCr2-xO3 (M = Co, Ni, Mn, Fe) inverted core-shell nanoparticles. This typically results in the formation of novel phases of MxCr2-xO3 shells having ferromagnetic/ferrimagnetic (FM/FiM) spin ordering and an antiferromagnetic (AFM) Cr2O3 core structure. The combined results from XRD and high-resolution TEM (HRTEM) provide evidence of the presence of corundum phase both in the shell and in the core regions. HRTEM results also show a sharp interface exhibiting epitaxial atomic registry of shell atoms over highly ordered core atoms whereas TEM-EDX analyses show that the M atoms reside predominantly in the shell regions. The XPS analyses of the NPs indicate the M transition metals incorporated in the shell are in the +2 oxidation state. Magnetic measurements show well developed hysteresis loops: The field cooled hysteresis loops reveal horizontal shifts in the applied field axis and vertical shifts in the magnetization axis, relative to the zero-field cooled hysteresis loops. This provides direct evidence for the exchange bias effect between the AFM α-Cr2O3 core and the FM/FiM α-MxCr2-xO3 shell. The XPS data are consistent with oxygen vacancy formation in order to maintain charge neutrality upon substitution of the M2+ ion for the Cr3+ ion in the α-MxCr2-xO3 shell. The FM/FiM ordering in the shell may at least partially result from the F-center exchange coupling between the oxygen-vacancy induced bound magnetic polaron and nearby cations.
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Sauceda-Oloño, Perla Yazmin, Hector Cardenas-Sanchez, Anya Isabel Argüelles-Pesqueira, Cindy Gutierrez-Valenzuela, Mario Enrique Alvarez-Ramos, Armando Lucero-Acuña, and Paul Zavala-Rivera. "Micelle Encapsulation of Ferromagnetic Nanoparticles of Iron Carbide@Iron Oxide in Chitosan as Possible Nanomedicine Agent." Colloids and Interfaces 4, no. 2 (May 22, 2020): 22. http://dx.doi.org/10.3390/colloids4020022.
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In this work, the synthesis and characterization of core/shell nanoparticles of iron carbide@iron oxide (Fe3C/γ-Fe2O3) encapsulated into micelles of sodium dodecylsulfate and oleic acid and stabilized with chitosan was developed. The materials were sonosynthesized at low intensities using standard ultrasonic baths with iron pentacarbonyl (Fe(CO)5) and oleic acid as iron source and hydrophobic stabilizer, respectively; obtaining nanoparticles with a hydrodynamic diameter of 19.71 nm and polydispersive index (PDI) of 0.13. The iron carbide@iron oxide nanoparticles (ICIONPs) in oleic acid were used as the organic phase during the self-assemble of nanoemulsion with sodium dodecylsulfate in water to obtain the metastable micelles. The final step involved the stabilization of the micelles using low molecular weight chitosan solution at 2% in acetic acid by ultrasonication bath. The nanosystem showed a hydrodynamic diameter of 185.30 nm, a PDI of 0.15 with a superficial charge ζ of 36.70 mV. Due to the magnetic, physical and chemical properties previously measured of the ICIONPs, it is believed that this type of nanoparticles can be used as a possible nanomedicine agent.
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Novosel, Nikolina, David Rivas Góngora, Zvonko Jagličić, Emil Tafra, Mario Basletić, Amir Hamzić, Teodoro Klaser, et al. "Grain-Size-Induced Collapse of Variable Range Hopping and Promotion of Ferromagnetism in Manganite La0.5Ca0.5MnO3." Crystals 12, no. 5 (May 19, 2022): 724. http://dx.doi.org/10.3390/cryst12050724.
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Among transition metal oxides, manganites have attracted significant attention because of colossal magnetoresistance (CMR)—a magnetic field-induced metal–insulator transition close to the Curie temperature. CMR is closely related to the ferromagnetic (FM) metallic phase which strongly competes with the antiferromagnetic (AFM) charge ordered (CO) phase, where conducting electrons localize and create a long range order giving rise to insulator-like behavior. One of the major open questions in manganites is the exact origin of this insulating behavior. Here we report a dc resistivity and magnetization study on manganite La1−xCaxMnO3 ceramic samples with different grain size, at the very boundary between CO/AFM insulating and FM metallic phases x=0.5. Clear signatures of variable range hopping (VRH) are discerned in resistivity, implying the disorder-induced (Anderson) localization of conducting electrons. A significant increase of disorder associated with the reduction in grain size, however, pushes the system in the opposite direction from the Anderson localization scenario, resulting in a drastic decrease of resistivity, collapse of the VRH, suppression of the CO/AFM phase and growth of an FM contribution. These contradictory results are interpreted within the standard core-shell model and recent theories of Anderson localization of interacting particles.
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Su, K. P., Zhong Wu Liu, X. X. Shan, Z. G. Zheng, X. C. Zhong, Hong Ya Yu, and De Chang Zeng. "Synthesis and Characterization of Core-Shell Structured Bimagnetic Cobalt-Coated Iron Nanoparticles." Materials Science Forum 688 (June 2011): 370–75. http://dx.doi.org/10.4028/www.scientific.net/msf.688.370.
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Core-shell structured nanoparticles with ferromagnetic core (Fe) and shell (Co) were prepared by a chemical reduction method. By adjusting the deposition parameters, the core-shell particles with various Fe:Co molar ratios were obtained. The saturation magnetization decreased with the increase of Cobalt content. The properties of core-shell nanoparticles synthesized under a magnetic field were compared with those prepared without a magnetic field. For the nanoparticles prepared without magnetic filed, the coercivity (Hc) increased with increasing Co content due to the large anisotropy of Co, whereas for the nanoparticles prepared under a magnetic field, theHcwas much lower. The ZFC/FC curves suggested that these particles were ferromagnetic at room temperature. The anisotropy constant K at 340K for core-shell nanoparticle is estimated to be 0.83×105erg/cm3. The second ferromagnetic phase transition may occur at the temperature lower than 25 K, which led to a drastic change of magnetization at low temperatures.
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Levshin, G. E. "WAYS TO IMPROVE INDUCTION CRUCIBLE FURNARES." Izvestiya. Ferrous Metallurgy 62, no. 2 (March 30, 2019): 97–102. http://dx.doi.org/10.17073/0368-0797-2019-2-97-102.
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Analysis of the main drawbacks caused by increased walls thickness of a lined crucible, presence of tubular copper single-layer inductor cooled from inside with standard water and absence or presence of core I-shaped magnetic circuits arranged around it forming a discrete ferromagnetic screen, was made for modern induction crucible furnaces. The first drawback is that a significant part of working electromagnetic flow Fwork is not used for effective heating, since it passes along the non-conductive lining of crucible, and not along the cage. Therefore, only 38.5 – 57.0 % of the flow Fwork is effectively used. The second drawback is increased cost and complexity of manufacturing of inductor coils from a special copper tube, which vibrate at twice the frequency, creating noise and weakening design of the furnace. Such inductors are characterized by reduced electrical efficiency and increased cost of preparation and cooling of conditioned water in systems that occupy an area several times greater than the area of furnace itself. The third drawback leads to the fact that a significant part of electromagnetic scattering flow of the Fconsupt does not participate in heating of charge and melt, but heats conductive elements of furnace, including surrounding magnetic inductor. Irrational use of total flow F, created by inductor, reduces its efficiency to almost 19 – 30 %, and the power factor cosφ to 0.03 – 0.10 and increases energy consumption. To reduce or eliminate disadvantages, three ways of improving these furnaces are proposed and justified: reducing thickness of crucible wall with its simultaneous hardening by installing a cylindrical shell between the crucible and the inductor, surrounding the inductor with an annular magnetic circuit and using a single or multiwire inductor instead of a tubular one. Combination of cylindrical shell, annular magnetic circuit, as well as the upper and lower plates of the furnace frame can form an annular closed cavity to accommodate wire inductor and circulating refrigerant, cooling the inductor and the magnetic circuit. As a result of the study, new design of induction crucible furnace with wire inductor and ring-type magnetic circuit developed at AltSTU is proposed, substantiated and patented. Based on experimental determination of effectiveness of the proposed structural elements, conclusion is made about the prospects for further research.
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Zhang, Ling, Ji Wei Zhai, Wei Feng Mo, and Xi Yao. "Dielectric and Magnetic Properties of CoFe2O4-BaTiO3 Composite Thick Film." Key Engineering Materials 421-422 (December 2009): 219–22. http://dx.doi.org/10.4028/www.scientific.net/kem.421-422.219.
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(x)CoFe2O4-(1-x) BaTiO3 thick film with x=0.2 was prepared by electrophoretic deposition technique using BaTiO3 and CoFe2O4 nanopowders. X-ray diffraction indicated the film was consisted of single spinel CoFe2O4 and perovskite BaTiO3 phase. The thick film exhibited good ferromagnetic and ferroelectric property. The dielectric properties were influenced by ferromagnetic phase, especially at low frequency and high temperature, which was attributed to space charge effects and Maxwell-Wagner relaxation.
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Sokol-Kutylovskii, Oleg. "Nonlinear amplification of the magnetic induction signal in a magnetomodulation sensor with an amorphous ferromagnetic core." Izvestiya VUZ. Applied Nonlinear Dynamics 30, no. 2 (March 31, 2022): 233–38. http://dx.doi.org/10.18500/0869-6632-2022-30-2-233-238.
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The purpose of this work is to show the possibility of using a magnetic field-controlled nonlinearity of the amplitude change in an oscillatory LC-circuit containing a core made of an amorphous ferromagnetic alloy with compensated longitudinal magnetostriction, which makes it possible to obtain a high conversion coefficient of weak magnetic field sensors operating at room temperature. Methods. A practical method for constructing magnetomodulation sensors of magnetic induction with a fixed magnetic displacement field, which corresponds to the maximum steepness of the nonlinear characteristic of an oscillatory circuit with an amorphous ferromagnetic core in the region of autoparametric resonance, is considered. Results. It has been shown that the stable conversion factor of a 35 mm long sensor based on an oscillatory circuit with autoparametric amplification at a modulation frequency of 256 kHz can reach 10 mV/nT, which allows, with the available element base, to record signals of a weak alternating magnetic field with an amplitude of 0.03 pT/Hz1/2 in the frequency range 10...1000 Hz. It is noted that the excitation of the sensor by a weak harmonic magnetic field of a high frequency and the constant presence of the amorphous ferromagnetic core near the state of technical saturation significantly reduces the level of intrinsic magnetic noise of the magnetomodulation sensor. Conclusion. Magnetomodulation sensors with autoparametric amplification of the magnetic induction signal can find application in geophysics, magnetobiology and biomedicine.
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Liu, Jing Song, You Chao Xu, and Tao Li. "Structure and Electrical Properties of PbTiO3-CoFe2O4 Magnetoelectric Composites." Materials Science Forum 687 (June 2011): 174–78. http://dx.doi.org/10.4028/www.scientific.net/msf.687.174.
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0-3 type magnetoelectric(ME) composites of PbTiO3(PT) and CoFe2O4(CFO) were prepared by a conventional solid-state reaction method with different volume fraction. The composites exhibited ferroelectric phase and ferromagnetic phase coexisting. The ferroelectric and magnetic properties of as-sintered samples were measured. The magnetic properties change regularly with the test frequency. But the dielectric permittivity shows the anomalies, which can be attributed to constraints and dilutions from the ferromagnetic phase and the element diffusion.
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Saragi, Togar, Bayu Permana, Arnold Therigan, Sahrul Hidayat, Norman Syakir, and Risdiana. "Physical Properties of Encapsulated Iron Oxide." Materials Science Forum 966 (August 2019): 277–81. http://dx.doi.org/10.4028/www.scientific.net/msf.966.277.
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The size effect of magnetic nanoparticles provides a various magnetic characteristic as a change of domain size. We report, synthesis of core-shell iron oxide and magnetic properties. Iron oxide particles were synthesized by co-precipitation method of iron (III) FeCl3.6H2O, iron (II) FeCl2.4H2O, in the mixture of with or without TEOS to investigated the physical properties. From XRD measurement, it was observed that all iron oxide particles with or without mixture of SiO2 has a hematite phase of a-Fe2O3. From M-H loop measurement, it was observed that the iron oxide without SiO2 has a ferromagnetic characteristic, while the iron oxide with SiO2 showed a medium state as a contribution of superparamagnetic and ferromagnetic properties.
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Chang, Ching-Hao, and Carmine Ortix. "Ballistic anisotropic magnetoresistance in core–shell nanowires and rolled-up nanotubes." International Journal of Modern Physics B 31, no. 01 (January 10, 2017): 1630016. http://dx.doi.org/10.1142/s0217979216300164.
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In ferromagnetic nanostructures, the ballistic anisotropic magnetoresistance (BAMR) is a change in the ballistic conductance with the direction of magnetization due to spin–orbit interaction. Very recently, a directional dependent ballistic conductance has been predicted to occur in a number of newly synthesized nonmagnetic semiconducting nanostructures subject to externally applied magnetic fields, without necessitating spin–orbit coupling. In this paper, we review past works on the prediction of this BAMR effect in core–shell nanowires (CSN) and rolled-up nanotubes (RUNTs). This is complemented by new results, we establish for the transport properties of tubular nanosystems subject to external magnetic fields.
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Samokhvalov, A. A., S. A. Evstigneeva, A. T. Morchenko, N. A. Yudanov, L. V. Panina, and M. G. Nematov. "Determination of small magnitudes of magnetostriction in amorphous microwires with an arbitrary type of magnetic anisotropy." Industrial laboratory. Diagnostics of materials 88, no. 1(I) (January 18, 2022): 62–68. http://dx.doi.org/10.26896/1028-6861-2022-88-1-i-62-68.
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The magnetic anisotropy and magnetic structure of amorphous ferromagnets are largely determined by magnetoelastic interactions due to the absence of magnetocrystalline anisotropy, e.g., in amorphous microwires with a glass sheath, the source of anisotropy is the mechanical stresses that arise in the ferromagnetic core upon manufacturing. Hence, to control the magnetic structure and magnetization reversal processes occurred in amorphous magnetics, it is necessary to know the magnetostriction coefficient of the material. We propose an improved approach to measuring extremely small values of the magnetostriction coefficient of ferromagnetic microwires with an arbitrary type of magnetic anisotropy and magnetic microstructure. The samples of amorphous wires in a glass sheath made of Co67Fe5B12Si14Cr3 alloys were studied. The type of magnetic anisotropy of the samples (from axial to circular) was changed using current annealing. The developed method is based on small-angle precession of magnetization around the wire axis, resulted from the effect of the axial magnetic field induced by an alternating current passed through the wire. A voltage signal generated in a detection coil wound around the sample at a frequency doubled with respect to the frequency of the alternating current was recorded using a lock-in amplifier. When exposed to external mechanical loads, the voltage signal changes, and an additional axial magnetic field (bias field) is required to maintain a constant level of this signal. The value of magnetostriction is determined from the dependence of the displacement field on mechanical loads. The maximum sensitivity of measurements in the range of 10–8 – 10–7 is achieved at a uniform magnetization, increased frequency of the alternating current, and high value of the ratio between the length and diameter of tested wire samples. The sign and magnitude of the magnetostriction constant change upon current annealing which correlates with modification of the magnetization curves. The results obtained can be used to determine and adjust the parameters of the actuators developed on the basis of the considered microwires (in particular, microsensors of mechanical stresses and microactuators).
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Guslienko, K. Yu. "Magnetic Vortex State Stability, Reversal and Dynamics in Restricted Geometries." Journal of Nanoscience and Nanotechnology 8, no. 6 (June 1, 2008): 2745–60. http://dx.doi.org/10.1166/jnn.2008.18305.
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Magnetic vortices are typically the ground states in geometrically confined ferromagnets with small magnetocrystalline anisotropy. In this article I review static and dynamic properties of the magnetic vortex state in small particles with nanoscale thickness and sub-micron and micron lateral sizes (magnetic dots). Magnetic dots made of soft magnetic material shaped as flat circular and elliptic cylinders are considered. Such mesoscopic dots undergo magnetization reversal through successive nucleation, displacement and annihilation of magnetic vortices. The reversal process depends on the stability of different possible zero-field magnetization configurations with respect to the dot geometrical parameters and application of an external magnetic field. The interdot magnetostatic interaction plays an important role in magnetization reversal for dot arrays with a small dot-to-dot distance, leading to decreases in the vortex nucleation and annihilation fields. Magnetic vortices reveal rich, non-trivial dynamical properties due to existance of the vortex core bearing topological charges. The vortex ground state magnetization distribution leads to a considerable modification of the nature of spin excitations in comparison to those in the uniformly magnetized state. A magnetic vortex confined in a magnetically soft ferromagnet with micron-sized lateral dimensions possesses a characteristic dynamic excitation known as a translational mode that corresponds to spiral-like precession of the vortex core around its equilibrium position. The translation motions of coupled vortices are considered. There are, above the vortex translation mode eigenfrequencies, several dynamic magnetization eigenmodes localized outside the vortex core whose frequencies are determined principally by dynamic demagnetizing fields appearing due to restricted dot geometry. The vortex excitation modes are classified as translation modes and radially or azimuthally symmetric spin waves over the vortex ground state. Studying the spin eigenmodes in such systems provides valuable information to relate the particle dynamical response to geometrical parameters. Unresolved problems are identified to attract attention of researchers working in the area of nanomagnetism.
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Li, Cui Xia, Zhi Hong Li, Xue Yan Du, and Hai Xia Guo. "Synthesis and Magnetic Properties of FePt /Silica Core-Shell Nanoparticles." Advanced Materials Research 178 (December 2010): 291–95. http://dx.doi.org/10.4028/www.scientific.net/amr.178.291.
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FePt nanoparticles (NPS), ~2nm in diameter, were synthesized and then coated with silica (SiO2) shells ~1.5nm-thick using reverse micelles as nanoreactors. The silica-coated FePt core–shell (FePt @silica) NPS were characterized by direct techniques of transmission electron microscopy (TEM). The results showed that the silica shells prevented the aggregation in liquid comparing to their bare counterparts. The as-synthesized FePt@SiO2 NPS exhibited essential characteristics of superparamagnetic behavior, as investigated by a vibrating sample magnetometer (VSM). X-ray diffraction (XRD) studies proved that the annealing at 700 °C for 30min under argon atmosphere caused the crystal structure of FePt core to transform from disordered face centered cubic (fcc) to the chemically ordered L10 FePt with face-centered tetragonal (fct) structure. This phase transition caused the change of magnetic properties of the FePt@SiO2 particles from superparamagnetism to ferromagnetism.
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Zentkova, Maria, and Marian Mihalik. "The Effect of Pressure on Magnetic Properties of Prussian Blue Analogues." Crystals 9, no. 2 (February 20, 2019): 112. http://dx.doi.org/10.3390/cryst9020112.
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We present the review of pressure effect on the crystal structure and magnetic properties of Cr(CN)6-based Prussian blue analogues (PBs). The lattice volume of the fcc crystal structure space group Fm 3 ¯ m in the Mn-Cr-CN-PBs linearly decreases for p ≤ 1.7 GPa, the change of lattice size levels off at 3.2 GPa, and above 4.2 GPa an amorphous-like structure appears. The crystal structure recovers after removal of pressure as high as 4.5 GPa. The effect of pressure on magnetic properties follows the non-monotonous pressure dependence of the crystal lattice. The amorphous like structure is accompanied with reduction of the Curie temperature (TC) to zero and a corresponding collapse of the ferrimagnetic moment at 10 GPa. The cell volume of Ni-Cr-CN-PBs decreases linearly and is isotropic in the range of 0–3.1 GPa. The Raman spectra can indicate a weak linkage isomerisation induced by pressure. The Curie temperature in Mn2+-CrIII-PBs and Cr2+-CrIII-PBs with dominant antiferromagnetic super-exchange interaction increases with pressure in comparison with decrease of TC in Ni2+-CrIII-PBs and Co2+-CrIII-PBs ferromagnets. TC increases with increasing pressure for ferrimagnetic systems due to the strengthening of magnetic interaction because pressure, which enlarges the monoelectronic overlap integral S and energy gap ∆ between the mixed molecular orbitals. The reduction of bonding angles between magnetic ions connected by the CN group leads to a small decrease of magnetic coupling. Such a reduction can be expected on both compounds with ferromagnetic and ferrimagnetic ordering. In the second case this effect is masked by the increase of coupling caused by the enlarged overlap between magnetic orbitals. In the case of mixed ferro–ferromagnetic systems, pressure affects μ(T) by a different method in Mn2+–N≡C–CrIII subsystem and CrIII–C≡N–Ni2+ subsystem, and as a consequence Tcomp decreases when the pressure is applied. The pressure changes magnetization processes in both systems, but we expect that spontaneous magnetization is not affected in Mn2+-CrIII-PBs, Ni2+-CrIII-PBs, and Co2+-CrIII-PBs. Pressure-induced magnetic hardening is attributed to a change in magneto-crystalline anisotropy induced by pressure. The applied pressure reduces saturated magnetization of Cr2+-CrIII-PBs. The applied pressure p = 0.84 GPa induces high spin–low spin transition of cca 4.5% of high spin Cr2+. The pressure effect on magnetic properties of PBs nano powders and core–shell heterostructures follows tendencies known from bulk parent PBs.
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Zhao, Yanhang, Jingang Wang, Shoupeng Ban, Xueqi Hu, and Diancheng Si. "Design and theoretical analysis of current transformer based on B-dot planar printed circuit board coil." Sensor Review 37, no. 3 (June 19, 2017): 282–88. http://dx.doi.org/10.1108/sr-12-2016-0264.
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Purpose The purpose of this paper is to design a current transformer model based on the principle of B-dot. It can reflect the change of transmission line current and meet the requirement of automation and intelligence for current measurement in power system. Design/methodology/approach In this paper, a new type of current transformer is designed on the principle of B-dot, which has the structure of the inverse series of planar air core coils and the form of printed circuit board (PCB). With this structure, the current transformers can induce magnetic field quite well. The finite element simulation for the current transformer with n layers structure is conducted in the Maxwell, which help to optimize the design of the current transformer. Findings By setting up the experimental platform, the experiment of the current transformer is carried out. The results of the test show that the measurement accuracy can satisfy the requirement of measurement. Besides, the new current transformer has good transient characteristics and can meet the needs of the development of smart grid. Originality value The new type of current transformer is based on the principle of B-dot, which is designed with a new type of non-contact PCB hollow coil current transformer. It has no iron core, no ferromagnetic effect and the phenomenon of ferromagnetic resonance. It has great progress in its insulation performance, volume and bandwidth response. In addition, the planar hollow coil of the inverse series structure can make the structure more accurate.
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Lazov, Lyubomir, and Peter Uzunov. "MINIMIZING THE DETENT FORCE IN PERMANENT MAGNET LINEAR SYNCHRONOUS MOTOR FOR DRIVING OF 2D LASER MARKING TABLE." Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference 3 (June 15, 2017): 325. http://dx.doi.org/10.17770/etr2017vol3.2595.
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In this paper the research results for reducing the detent force in one innovative permanent magnet linear synchronous motor for 2D laser marking system was published. There two methods are used. The first of these methods features the usage of two additional end teeth with chamfers in the magnetic circuit of the movable part. In the second method, the teeth of the ferromagnetic core are with different lengths. As a result of the change of the air gap permeance in both cases substantial reduction of detent force is achieved, in multiples at times. The results obtained are based on modeling and analyzing the linear motor magnetic field by the Finite Element Method (FEM). Provided experimental research of the linear motor prototype proves the correctness of the simulations results.
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Lazov, Lyubomir, and Peter Uzunov. "MINIMIZING THE DETENT FORCE IN PERMANENT MAGNET LINEAR SYNCHRONOUS MOTOR FOR DRIVING OF 2D LASER MARKING TABLE." Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference 3 (June 15, 2017): 174. http://dx.doi.org/10.17770/etr2017vol3.2651.
Full textAbstract:
In this paper the research results for reducing the detent force in one innovative permanent magnet linear synchronous motor for 2D laser marking system was published. There two methods are used. The first of these methods features the usage of two additional end teeth with chamfers in the magnetic circuit of the movable part. In the second method, the teeth of the ferromagnetic core are with different lengths. As a result of the change of the air gap permeance in both cases substantial reduction of detent force is achieved, in multiples at times. The results obtained are based on modeling and analyzing the linear motor magnetic field by the Finite Element Method (FEM). Provided experimental research of the linear motor prototype proves the correctness of the simulations results.
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Varma, Ramesh R., Purnima S. Sengunthar, Nikhil G. Joshi, M. R. Gadhvi, U. V. Chhaya, and Utpal S. Joshi. "Synthesis and Electrical Properties of 1-x(Na0.5K0.5NbO3)-x(CoFe2O4)." Solid State Phenomena 209 (November 2013): 66–69. http://dx.doi.org/10.4028/www.scientific.net/ssp.209.66.
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Magnetoelectric (ME) effect is a coupled two-field effect in which application of an electric field induces magnetization and a magnetic field induces electrical polarization. However, it is difficult for a single material to have this combination of the ferromagnetic and ferroelectric properties. Thus, ferromagnetic–ferroelectric/dielectric composite materials become an attractive subject. Na1−xKxNbO3(NKN) is a combination of ferroelectric KNbO3and antiferroelectric NaNbO3, and forms a morphotropic phase boundary (MPB) near 50/50 composition (x=0.50) separating two orthorhombic phases. NKN has high electromechanical coupling coefficient (k2) and high phase transition temperature (Tc = 425 °C), especially near the morphotropic phase boundary (MPB). CoFe2O4(CFO), on the other hand, is well known spinel ferrite with high Curie temperature. We have synthesized ceramic composites, 1-x(Na0.5K0.5NbO3)-x(CoFe2O4) with x = 0.0 to 1.0 (in step of 0.2) by standard solid state reaction route. Powder XRD show a mixed cubic phase without impurity peaks for the samples under study. In low frequency range the dielectric properties of the NKN/CFO composites show Maxwell–Wagner relaxation. Systematic change in the electrical polarization with increasing x was observed at various applied fields at room temperature.
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Hu, Y., Y. Liu, and A. Du. "The effect of a cooling field on exchange bias in a nanoparticle system." Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanoengineering and Nanosystems 222, no. 1 (March 1, 2008): 17–22. http://dx.doi.org/10.1243/17403499jnn131.
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Interest in exchange bias in magnetic nanoparticles has increased in the past few years by virtue of its potential for applications in fields such as ultrahigh-density magnetic recording. A modified Monte Carlo Metropolis method is employed to simulate the effect of cooling field on exchange bias and coercivity of a granular system of ferromagnetic nanoparticles embedded in an antiferromagnetic matrix, based on the classical three-dimensional Heisenberg model. The results show that the exchange bias is constantly negative, and that its absolute value decreases to a metastable value initially, while the coercivity increases monotonically with increase in the cooling field, and they both level off as the cooling field gains sufficient strength. The phenomena can be attributed to the energy barriers arising from the high antiferromagnetic anisotropy and the frustrated core—matrix structure. However, the interfacial coupling may change the configuration of the antiferromagnetic matrix to influence the exchange bias.
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Zhang, Xiangyong, Haipeng Liu, Yunli He, Tingrui Peng, Bin Su, and Huiyuan Guan. "Analysis of the Influence of Ferromagnetic Material on the Output Characteristics of Halbach Array Energy-Harvesting Structure." Micromachines 12, no. 12 (December 11, 2021): 1541. http://dx.doi.org/10.3390/mi12121541.
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Due to the particular arrangement of permanent magnets, a Halbach array has an significant effect of magnetism and magnetic self-shielding. It can stretch the magnetic lines on one side of the magnetic field to obtain an ideal sinusoidal unilateral magnetic field. It has a wide application range in the field of energy harvesting. In practical applications, magnetic induction intensity of each point in magnetic field is not only related to the induced current and conductor but also related to the permeability of the medium (also known as a magnetic medium) in the magnetic field. Permeability is the physical quantity that represents the magnetism of the magnetic medium, which indicates the resistance of magnetic flux or the ability of magnetic lines to be connected in the magnetic field after coil flows through current in space or in the core space. When the permeability is much greater than one, it is a ferromagnetic material. Adding a ferromagnetic material in a magnetic field can increase the magnetic induction intensity B. Iron sheet is a good magnetic material, and it is easy to magnetize to generate an additional magnetic field to strengthen the original magnetic field, and it is easy to obtain at low cost. In this paper, in order to explore the influence of ferromagnetic material on the magnetic field and energy harvesting efficiency of the Halbach array energy harvesting structure, iron sheets are installed on the periphery of the Halbach array rotor. Iron sheet has excellent magnetic permeability. Through simulation, angle between iron sheet and Halbach array, radian size of iron sheet itself and distance between iron sheet and Halbach array can all have different effects on the magnetic field of the Halbach array. It shows that adding iron sheets as a magnetic medium could indeed change the magnetic field distribution of the Halbach array and increase energy harvesting efficiency. In this paper, a Halbach array can be used to provide electrical power for passive wireless low-power devices.
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Sivaraj, K. S., S. Thoufeeq, and M. R. Anantharaman. "Effect of chromium substitution on the electrical and magnetic properties of multiferroic yttrium manganite." Physica Scripta 97, no. 3 (February 16, 2022): 035807. http://dx.doi.org/10.1088/1402-4896/ac520e.
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Abstract Yttrium Manganite is a multiferroic material and has potential applications in Ferroelectric Random Access Memories. Chromium is substituted with a view to enhancing the electrical conductivity. Compositions belonging to the series Y1−xCrxMnO3, (x = 0, 0.05, 0.1, and 0.3) were synthesized by employing a citrate gel method. Pre characterized samples using X-ray diffraction and Scanning Electron Microscopy were then subjected to impedance spectroscopy to understand the conduction mechanism vis-à-vis small polaron hopping or variable range hopping. Cole-Cole and Nyquist plots were utilized to arrive at the equivalent circuit. Ferroelectric measurements were carried out to understand the polarization mechanisms. Magnetic measurements were also conducted to observe the change in magnetic properties with Chromium substitution. Field Cooled (FC) and Zero Field Cooled (ZFC) magnetization measurements revealed the presence of ferromagnetic clusters in an antiferromagnetic matrix. It has been found that Chromium substitution enhances the electrical conductivity while it diminishes the ferroelectric properties.
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Vukotić, Mario, Danijel Rodić, Boris Benedičič, and Damijan Miljavec. "Cogging torque in slotless permanent magnet machines." Journal of Electrical Engineering 71, no. 3 (June 1, 2020): 195–202. http://dx.doi.org/10.2478/jee-2020-0026.
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AbstractSlotless permanent magnet machines theoretically do not produce any cogging torque, provided the stator inner surface reluctance remains unchanged. However, a cogging torque may occur due to a change in the electromagnetic design following material cost reduction in the manufacturing process. When the electromagnetic design is changed to reduce the waste in the manufacturing process (stamping of the laminations) by dividing the stator toroidal ferromagnetic core into two equal parts, gluing them together introduces a very small non magnetic gap between them, which affects the stored magnetic energy along the circumference and consequently gives rise to occurrence of a cogging torque. Using the finite element method its value is analyzed analytically and verified by a laboratory measurement. Results of our work, presented in this paper, will help scientists and engineers to understand and avoid the causes for the occurrence of the cogging torque in designing slotless permanent magnet machines, where the design itself is subjected to the manufacturing process.
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Bhaktha, Sandesh, Sriharsha Hegde, and Sathish Rao U. "Experimental Analysis of Viscoelastic Properties of Room Temperature Vulcanized Silicone based Magnetorheological Elastomer." Defence Science Journal 72, no. 1 (January 5, 2022): 98–104. http://dx.doi.org/10.14429/dsj.72.17089.
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Magnetorheological Elastomers (MRE) endure a change in mechanical properties with the application of an externally applied magnetic field. It consists of an elastomeric matrix reinforced with ferromagnetic powdered particles. This paper focuses on the investigation of viscoelastic properties of Room Temperature Vulcanized (RTV) silicone based isotropic MRE in sandwich beam configuration by varying the volume percentage of Carbonyl Iron Powdered (CIP) reinforcement. Viscoelastic properties of the MRE core material were calculated by following the ASTM E756-05 standard. The magnetic field was applied by employing a Halbach array which was numerically analyzed using Finite Element Method Magnetics (FEMM). The magnetic field was varied up to 0.15 T. Loss factor and shear modulus were found to be strongly influenced by the percentage content of CIP. The loss factor and shear modulus of 30% MRE at 0.15 T were higher than other tested samples. The variation of natural frequency with respect to the addition of CIP was validated numerically using Modal analysis conducted in Hyperworks.
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Mubarak, A. A. "The mechanical, optical and thermoelectric properties of MCoF3 (M = K and Rb) compounds." Modern Physics Letters B 31, no. 06 (February 28, 2017): 1750033. http://dx.doi.org/10.1142/s0217984917500336.
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This is an ab initio study instituted on the density functional theory (DFT) and the full-potential linearized augmented plane wave (FP-LAPW) calculations that are performed to analyze the mechanical, electronic, optical and thermoelectric properties of the cubic MCoF3 compound (M = K and Rb). The studied compounds are found thermodynamically and mechanically stable. Moreover, these compounds are found to be elastically anisotropic and ductile. KCoF3 and RbCoF3 are classified as half-metallic and anti-ferromagnetic compounds. The optical properties are investigated from the dielectric function for the different energy ranges. The thermoelectric properties such as transport properties are determined as a function of temperature using BoltzTrape code in the range of 20–800 K. The present compounds are found to have p-type character. Also, the majority charge carriers are found to be electrons rather than hole. Useful mechanical, spintronic, optical and thermoelectric applications are predicted based upon the calculations.
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Laundy, D., S. Brown, M. J. Cooper, D. Bowyer, P. Thompson, D. F. Paul, and W. G. Stirling. "Magnetism in Nickel and Synchrotron Beam Polarization Studied by X-ray Diffraction." Journal of Synchrotron Radiation 5, no. 4 (July 1, 1998): 1235–39. http://dx.doi.org/10.1107/s0909049597019420.
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The ratio of the magnetic to the charge form factors of nickel has been determined by white-beam X-ray diffraction. The measurements were made on the new UK magnetic scattering beamline (XMaS) on a dipole source at the ESRF. The data comprise the three (h,h,0) reflections (4,4,0), (6,6,0) and (8,8,0) and the seven high-order (h,0,0) reflections (6,0,0) to (18,0,0), which doubles the range of wavevectors compared to previous studies. The data have been analysed using Hartree–Fock free-ion wave functions and core electron polarization effects were included. The results support the interpretation of neutron data obtained at lower momentum transfer for the e g and t 2g orbital occupancies. The polarization of the dipole source is deduced to vary from 99.88 to 99.83% between 5 and 15 keV, respectively. This high value makes it an extremely suitable source for studies of ferromagnetism.
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Mubarak, A. A. "First principles calculations of the electronic, optical and thermoelectric performance of RbZn1−x NixF3 (x = 0, 0.25, 0.5, 0.75 and 1) alloys." International Journal of Modern Physics B 33, no. 14 (June 10, 2019): 1950141. http://dx.doi.org/10.1142/s0217979219501418.
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First principles investigations of the electronic, optical and thermoelectric performance of RbZn[Formula: see text]Ni[Formula: see text]F3 (x = 0, 0.25, 0.5, 0.75 and 1) alloys are calculated using spin polarized full-potential linear augmented plane wave method, as implemented in Wien2k code. These alloys are found to be stable, ductile and can be formed with ferromagnetic character. RbZn[Formula: see text]Ni[Formula: see text]F3 are found to be insulator alloys with bandgap energy of range 7.02–5.14 eV using the modified Becke–Johnson functional. This gap is decreasing with increasing the Ni concentration in the unit cell. The optical parameters are calculated in the energy range upto 35 eV. The calculated static refractive index values are found directly proportional with the higher concentration of Ni atoms in the alloys. The transport coefficients are calculated using BoltzTrap code. The hole assumes the main charge carriers of the present alloys with p-type-doping for RbZnF3 alloy and n-type-doping for RbZn[Formula: see text]Ni[Formula: see text]F3. The calculated optical and transport coefficient values show promising optoelectronic and thermoelectric applications of the studied alloys.
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Chauhan, Samta, Saurabh Kumar Srivastava, Amit Singh Rajput, and Ramesh Chandra. "Effect of Gd-substitution at Y-site on the structural, magnetic and dielectric properties of Y1-xGdxMnO3 (x=0, 0.05) nanoparticles." MRS Proceedings 1675 (2014): 121–28. http://dx.doi.org/10.1557/opl.2014.874.
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ABSTRACTEffect of Gd substitution at Y-site on the structural and magnetic properties of Y1-xGdxMnO3 (x=0, 0.05) nanoparticles prepared by conventional solid state reaction method has been studied. The structural study using X-ray diffraction pattern indicates the hexagonal structure with P63cm space group for all the samples. The average particle size for all the samples lies in the range of 30-40 nm as confirmed by X-ray diffraction and transmission electron microscopy analysis. The change in a and c lattice parameters confirm the substitution of Gd at Y-site. Magnetization versus temperature measurements show enhanced magnetic moment and an increase in Neel temperature with Gd-doping. Spin glass behavior is observed at low temperature in all the samples. Exchange bias effect has been observed at 5 K after field cooling the samples which is ascribed to the formation of antiferromagnetic-ferromagnetic (AFM-FM) core-shell structure of the nanoparticles. A significant improvement in the dielectric properties of Gd-doped samples has also been observed.
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Di, Yong Jiang, Jun Wang, Deng Ming Chen, Bi Jia, and Jian Jun Jiang. "Effect of Annealing on the Magnetostatic and Microwave Electromagnetic Properties of Glass-Coated Fe-Rich Microwires." Advanced Materials Research 562-564 (August 2012): 345–49. http://dx.doi.org/10.4028/www.scientific.net/amr.562-564.345.
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Glass-coated FeCuNbVSiB microwires was annealed in the temperature range of 380 °C to 600 °C. The microstructures and magnetostatic properties of the glass-coated microwires were characterized by X–ray diffraction (XRD), Vibrating Sample Magnetometer (VSM) respectively. Relative complex permeability and complex permittivity was measured by transmission/reflection (T/R) coaxial line method in the frequency range of 2-18 GHz for as-casted and annealed Fe-rich microwires samples. The measured results show that the coercive field of the Fe-rich microwires decrease to 1.54 Oe at 470 °C, and then increase rapidly with the increasing of the annealing temperature. The coercive field and saturation field of the microwire samples increased abruptly with the outgrowth of the Fe-B hard magnetic phase in the Fe-rich microwire samples. The imaginary part of permeability and the natural ferromagnetic resonance frequency decrease for the thermal treatment below 470 °C, and then increase with the annealing temperature up to 530 °C. The change of magnetostatic and microwave electromagnetic properties of the microwires samples with the annealing process come from the change of the anisotropy caused by the internal stress.
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Franco, Nuno, Eduardo Alves, M. Rickart, Anibal Guedes, Paulo Freitas, and Nuno P. Barradas. "X-Ray Diffraction Study of Ordered Antiferromagnets for Tunnel Junctions." Materials Science Forum 514-516 (May 2006): 314–18. http://dx.doi.org/10.4028/www.scientific.net/msf.514-516.314.
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Antiferromagnets (AF) such as MnPt and MnNi can be used in spin valves and tunnel junctions due to their high exchange coupling, high blocking temperature, and fair corrosion resistance. They are used as pinning layer in a AF/FM/barrier/FM structure, where FM is a ferromagnet such as CoFe and the barrier is an ultra-thin insulating layer. However, as deposited MnPt and MnNi films with thickness around 20 nm are in the fcc phase, and show no exchange bias in AF/FM bilayers. A transition from fcc to fct is required, and takes place upon annealing. We present an X-ray diffraction study of the phase transition in glass/Ta 7nm/Ru 3 nm/MnPt 20 nm/CoFe 5 nm/Ta 3 nm AF/FM bilayers. We observe the MnPt phase transition from fcc to fct around 250°C. We correlate the phase transition with the change of the bilayers magnetic properties.
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RIZWAN, SYED, H. F. LIU, X. F. HAN, SEN ZHANG, Y. G. ZHAO, and S. ZHANG. "ELECTRIC-FIELD CONTROL OF GIANT MAGNETORESISTANCE IN SPIN-VALVES." SPIN 02, no. 01 (March 2012): 1250006. http://dx.doi.org/10.1142/s2010324712500063.
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It has been known that magnetic properties of a ferromagnet grown on piezoelectric substrates can be altered by the electric field-induced strain. We consider spin-valve CoFe/Cu/CoFe/IrMn grown on (011)-cut piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) substrate and investigate the effect of the electric field on the giant magnetoresistance (GMR) of the spin valve. We found that the electric field induced strain on PMN–PT substrate enhances the coercivity of the magnetic layers. The transport measurement shows that the GMR ratio of the spin valve could be altered as much as 50% for an electric field of -8 kV/cm. The change of GMR is attributed to the reduced maximum degree of the antiparallel alignment between the magnetization directions of the free and pinned layers. The present studies establish a prototype electrically tunable magnetic memory device such that the electric field can reversibly tune spin valve magnetoresistance without deteriorating electric and magnetic properties.
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Goswami, Partha. "Fermions on the low-buckled honey-comb structured lattice plane and classical Casimir–Polder force." International Journal of Modern Physics B 30, no. 16 (June 23, 2016): 1650087. http://dx.doi.org/10.1142/s0217979216500879.
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We start with the well-known expression for the vacuum polarization and suitably modify it for 2[Formula: see text]1-dimensional spin–orbit coupled (SOC) fermions on the low-buckled honey-comb structured lattice plane described by the low-energy Liu–Yao–Feng–Ezawa (LYFE) model Hamiltonian involving the Dirac matrices in the chiral representation obeying the Clifford algebra. The silicene and germanene fit this description suitably. They have the Dirac cones similar to those of graphene and SOC is much stronger. The system could be normal or ferromagnetic in nature. The silicene turns into the latter type if there is exchange field arising due to the proximity coupling to a ferromagnet (FM) such as depositing Fe atoms to the silicene surface. For the silicene, we find that the many-body effects considerably change the bare Coulomb potential by way of the dependence of the Coulomb propagator on the real-spin, iso-spin and the potential due to an electric field applied perpendicular to the silicene plane. The computation aspect of the Casimir–Polder force (CPF) needs to be investigated in this paper. An important quantity in this process is the dielectric response function (DRF) of the material. The plasmon branch was obtained by finding the zeros of DRF in the long-wavelength limit. This leads to the plasmon frequencies. We find that the collective charge excitations at zero doping, i.e., intrinsic plasmons, in this system, are absent in the Dirac limit. The valley-spin-split intrinsic plasmons, however, come into being in the case of the massive Dirac particles with characteristic frequency close to 10 THz. Our scheme to calculate the Casimir–Polder interaction (CPI) of a micro-particle with a sheet involves replacing the dielectric constant of the sample in the CPI expression obtained on the basis of the Lifshitz theory by the static DRF obtained using the expressions for the polarization function we started with. Though the approach replaces a macroscopic constant by a microscopic quantity, it has the distinct advantage of the many-body effect inclusion seamlessly. We find the result that for the nontrivial susceptibility and polarizability values of the sheet and micro-particle, respectively, there is crossover between attractive and repulsive behavior. The transition depends only on these response functions apart from the ratio of the film thickness and the micro-particle separation ([Formula: see text]/[Formula: see text]) and temperature. Furthermore, there is a longitudinal electric field induced topological insulator (TI) to spin-valley-polarized metal (SVPM) transition in silicene, which is also referred to as the topological phase transition (TPT). The low-energy SVP carriers at TPT possess gapless (massless) and gapped (massive) energy spectra close to the two nodal points in the Brillouin zone with maximum spin-polarization. We find that the magnitude of the CPF at a given ratio of the film thickness and the separation between the micro-particle and the film are greater at TPT than at the TI and trivial insulator phases.
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Al-Elaimi, Mahmoud, Farida Hamioud, G. I. Ameereh, and A. A. Mubarak. "Theoretical investigation of the electronic and thermoelectric behavior of CoV2O4 alloy." International Journal of Computational Materials Science and Engineering 08, no. 02 (June 2019): 1950008. http://dx.doi.org/10.1142/s2047684119500088.
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Density functional theory (DFT) within Wien2k code is utilized to compute the mechanical, thermal, electronic, magnetic and thermoelectric properties of the cubic spinel CoV2O4. The ground state lattice constant of CoV2O4 alloy agrees with previous literature. The calculated elastic constants of CoV2O4 predict that the present alloy is anisotropic, elastically stable and brittle. Beneficial acoustical applications are expected for the present alloy due to its high calculated Debye temperature and average sound velocities values. The longitudinal and transverse sound velocities modes of vibrations are found maximum along [110] directions compared to [100] and [111] directions. The calculated DOS and band structure show that CoV2O4 is electronically stable. The present alloy possesses a total magnetic moment of 12.0 [Formula: see text] and is classified as a half-metallic ferromagnet. CoV2O4 shows [Formula: see text]-type behavior and favors holes as charge carriers. The present alloy owns beneficial thermoelectric properties and can be used in thermoelectric applications.
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Pascale, Fabien, Philippe D’Arco, Valentina Lacivita, and Roberto Dovesi. "The superexchange mechanism in crystalline compounds. The case of KMF3 (M = Mn, Fe, Co, Ni) perovskites." Journal of Physics: Condensed Matter 34, no. 7 (November 23, 2021): 074002. http://dx.doi.org/10.1088/1361-648x/ac36fe.
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Abstract The ferromagnetic and antiferromagnetic wavefunctions of four KMF3 (M = Mn, Fe, Co and Ni) perovskites have been obtained quantum-mechanically with the CRYSTAL code, by using the Hartree–Fock (HF) Hamiltonian and three flavours of DFT (PBE, B3LYP and PBE0) and an all-electron Gaussian type basis set. In the Fe and Co cases, with d6 and d7 occupation, the Jahn–Teller distortion of the cubic cell is as large as 0.12 Å. Various features of the superexchange interaction energies (SIE), namely additivity, dependence on the M–M distance, on the M F M ̂ angle, and on the adopted functional, are explored. The contribution to SIE by the Coulomb, exchange and kinetic energy terms is analyzed. It is shown that, when using density functionals, SIE clearly correlates with the amount of exact (Hartree–Fock) exchange in the functional. The effect of SIE on the equilibrium geometry and volume of the unit cell is discussed, and it is shown that the key quantity is the spin polarization of the (closed shell) F ions along the M–F–M path. The effect of this magneticpressure is evaluated quantitatively for the first time. The superexchange coupling constant J, evaluated at the HF level and through the Ising model, underestimates the experimental values by about 60%–70%. The more sophisticated Yamaguchi model (that takes into account the contamination of the FM and AFM spin states) does not reduce the discrepancy. The B3LYP hybrid functional overestimates the experiments. These last are bracketed by HF and PBE0. For PBE, the overestimation is huge. Finally, Mulliken population data, charge and spin density maps and density of states are used to illustrate the electronic structure.
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Ang, R., Y. P. Sun, G. H. Zheng, and W. H. Song. "Magnetic, electrical, and thermal characterization of La0.9Te0.1Mn1−xCoxO3 (0 ≤ x ≤ 1)." Journal of Materials Research 22, no. 10 (October 2007): 2943–52. http://dx.doi.org/10.1557/jmr.2007.0379.
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The structure, magnetization M, resistivity ρ, thermoelectric power S, and thermal conductivity κ in La0.9Te0.1Mn1−xCoxO3 (0 ≤ x ≤ 1) have been investigated systematically. The samples with x = 0 and x = 1 have a rhombohedral lattice with space group R¯3C, while the samples with x = 0.25, 0.50, and 0.75 have an orthorhombic lattice with space group Pbnm. The samples of 0 ≤ x ≤ 0.75 undergo the paramagnetic–ferromagnetic (PM–FM) phase transition. Based on the temperature dependence of susceptibility, a combination of the high-spin (HS) state for Co2+ and the low-spin (LS) state for Co3+ can be determined. The metal–insulator transitions (MIT) observed for x = 0 sample are completely suppressed with Co-doping, and ρ(T) displays semiconducting behavior within the measured temperature region for x > 0 samples. As x ⩾ 0.25, the huge magnitude of Seebeck coefficient at low temperatures is observed, which is suggested to originate from the spin-state transition of Co3+ ions from intermediate-spin (IS) state or (HS) state to (LS) state and the configurational entropy of charge carriers enhanced by their spin and orbital degeneracy between Co2+ and Co3+ sites. Particularly, S(T) of x = 0.50 and 0.75 samples appears an anomalous peak, which is suggested to be related to the contribution of phonon drag. Similar to M(T) and ρ(T), all results of S(T) are discussed according to the variations of the structure parameters and magnetic exchange interaction caused by Co-doping. In addition, based on the analysis of the temperature dependence of S(T) and ρ(T), the transport mechanism can be determined in the different temperature region. As to thermal conduction κ(T), the changes of κ with Co-doping is suggested to come from the combined effect due to the suppression of local Mn3+O6 Jahn–Teller (JT) lattice distortion because of the substitution of non JT Co3+ ions with LS and HS states for JT Mn3+ ions, which results in the increase of κ, and the introduction of the disorder due to Co-doping, which contributes to the decrease of κ.
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Lesniewska, Elzbieta. "Immunity of current-to-voltage transducer, with coils manufactured by means of multilayered PCB technology, to external magnetic fields." COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering 34, no. 4 (July 6, 2015): 1156–71. http://dx.doi.org/10.1108/compel-07-2014-0180.
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Purpose – The purpose of this paper is to discuss the operation of new generation electromagnetic current-to-voltage transducer. The aim of research was analysis of behaviour of considered current-to-voltage transducers during operation. The main problem was to estimate whether the external fields are able to change the value of the secondary voltage and that the replacement of the casing material by a conductive or ferromagnetic material will increase the immunity of the transducer to external magnetic fields. The immunity of current-to-voltage transducers to the external fields is very important because it influences the proper functioning of the protection system. Design/methodology/approach – The use of analytical methods to assess the influence of external fields was impossible due to the complexity of the geometry. The 3D computations were necessary because of different cross sections of circuit boards at different heights. Therefore the numerical 3D field-and-circuit method based on finite element method was applied. The wide range of dimensions in computation system, ranging from 0.15 mm (print paths) to 0.22 m, made it necessary to use the mesh of millions of elements. The division of this type of system into elements requires a diverse and extremely dense mesh in the area of printed circuits board (PCBs). Findings – The 3D analysis of magnetic field distribution was performed for different external field effect upon a current-to-voltage transducer. The magnetic field distributions and the induced secondary voltage for several different cases were presented. As a conclusion it can be said that in this particular case the magnetic shield is most effective. The influence of external magnetic fields caused by currents passing through the other neighbouring phase bars near are insignificant for the transducer with non-magnetic core. Practical implications – Commonly used in measuring and protection systems of the transmission lines are induction instrument transformers. The instrument transformers are very precise devices and their errors are counted in tenths of a per cent, and phase displacement of signals in minutes. Especially in HV systems they are very big and their cores are heavy. Replacement of instrument transformers by the current to voltage transducers cooperating with electronic measuring systems will reduce the size and cost of devices. Originality/value – The requirements set for protective current transformers concern the transformation of currents, with high accuracy, especially at transient states. Therefore magnetic characteristics of their cores should be linear. It causes that cores are large and have some air gaps. Current-to-voltage transducers based on Rogowski coil are particularly suitable for the replacement of the protective current transformers because of their linearity. The traditional technologies used for making Rogowski coil consisted in winding a wire on a non-magnetic carcass. The development of technology has enabled the use of new technologies PCB high density interconnect in the production of Rogowski coil.
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Wu, Hao, Aitian Chen, Peng Zhang, Haoran He, John Nance, Chenyang Guo, Julian Sasaki, et al. "Magnetic memory driven by topological insulators." Nature Communications 12, no. 1 (October 29, 2021). http://dx.doi.org/10.1038/s41467-021-26478-3.
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AbstractGiant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 105 A cm−2 have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiency θSH in TIs is quantified by both the SOT-induced shift of the magnetic switching field (θSH = 1.59) and the SOT-induced ferromagnetic resonance (ST-FMR) (θSH = 1.02), which is one order of magnitude larger than that in conventional heavy metals. These results inspire a revolution of SOT-MRAM from classical to quantum materials, with great potential to further reduce the energy consumption.
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Abdulvagidov, Shapiullah B., Shamil Z. Djabrailov, and Belal Sh Abdulvagidov. "Nature of novel criticality in ternary transition-metal oxides." Scientific Reports 9, no. 1 (December 2019). http://dx.doi.org/10.1038/s41598-019-55594-w.
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AbstractThere are the chains of transition-metal cations alternating with the anions of oxygen in ternary transition-metal oxides. When a p-orbital of the oxygen connects the half-filled and empty d-orbitals of adjacent transition-metal cations, double-exchange ferromagnetism takes place. Although double exchange has been well explored, the nature of novel criticality, induced by it, is yet not uncovered. We explored the magnetic-field scaling in the heat capacity of a Sm0.55Sr0.45MnO3 manganite, one of the best ternary transition-metal oxides as it is completely ferromagnetic, and found novel criticality - unordinary critical exponents which are the consequence of coherence of Coulomb lattice distortion and ferromagnetism. The coherence is caused by the trinity of the mass, the charge and the spin of an electron. When the d and p orbitals overlaps, it quickly walks from one site to the another due its lightest mass. And due to its electric charge, it equalizes the valences of the transition-metal cations in the chains and so diminishes the Coulomb lattice distortion. At last, its spin forces magnetic moments of transition-metal cations to ferromagnetically arrange. The disappearance of Coulomb distortions widens the overlap and lowers the elastic lattice energy, so that not only the spin of an electron, but also its electric charge strengthens ferromagnetism. That nonlinear effect strengthens the critical behaviour and critical exponents come off any known universality classes. Thus, the symbiotic coherence of annihilating Coulomb distortions and arising ferromagnetism is a reason of the novel criticality.
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Rawat, Dipti, P. B. Barman, and Ragini Raj Singh. "Corroboration and efficacy of Magneto-Fluorescent (NiZnFe/CdS) Nanostructures Prepared using Differently Processed Core." Scientific Reports 9, no. 1 (October 22, 2019). http://dx.doi.org/10.1038/s41598-019-51631-w.
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Abstract The selected and controlled preparation of core@shell nanostructures, which unite the multiple functions of ferromagnetic Ni-Zn ferrite core and CdS shell in a single material with tuneable fluorescence and magnetic properties, have been proposed by the seed mediated aqueous growth process. The shell particle thickness and core of nanostructures were precisely tuned. Current work exhibits the comparative study of core@shell multifunctional nanostructures where core being annealed at two different temperatures. The core@shell nanostructure formation was confirmed by complementary structural, elemental, optical, magnetic and IR measurements. Optical and magnetic characterizations were performed to study elaborative effects of different structural combinations of core@shell nanostructures to achieve best configuration with high-luminescence and magnetic outcomes. The interface of magnetic/nonmagnetic NiZnFe2O4/CdS nanostructures was inspected. Unexpectedly, in some of the core@shell nanostructures presence of substantial exchange-bias was observed in spite of the non-magnetic nature of CdS QDs which is clearly an “optically-active” and “magnetically-inactive” material. Presence of “exchange-bias” was confirmed by the change in “magnetic-anisotropy” as well as shift in susceptibility derivative. Finally, successful formulation of stable and efficient core@shell nanostructures achieved, which shows no exchange-bias and shift. Current findings suggest that these magneto-fluorescent nanostructures can be used in spintronics; and drug delivery-diagnosis-imaging applications in nanomedicine field.
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Sun, N. X., A. M. Crawford, and S. X. Wang. "Advanced Soft Magnetic Materials for Magnetic Recording Heads and Integrated Inductors." MRS Proceedings 721 (2002). http://dx.doi.org/10.1557/proc-721-e6.3.
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AbstractHigh performance magnetic heads, inductors and transformers, indispensable to information technology encompassing from information storage, portable power delivery, to wireless communication, require soft magnetic films with low coercivities, high permeability, and large ferromagnetic resonance frequencies.The Fe-Co-N-based films have a ferromagnetic resonance frequency of >1 GHz at zero-bias field, showing great promise for applications in write heads and integrated inductors in a frequency range of >1 GHz. Magnetization dynamics measurements at sub-nanosecond scale have been performed on Fe-Co-N high saturation soft magnetic films with Permalloy nanolayer seeds having a saturation magnetization of 24 kG. The high frequency behavior appears to be affected by magnetic anisotropy dispersion.One of the biggest challenges facing integration of magnetic material onto silicon is the compatibility of magnetics with standard silicon processing techniques. Integrated inductors were realized using ground planes of Co-Ta-Zr (p=100μΩ-cm). The magnetic properties of Co-Ta-Zr showed no change even after undergoing high temperature processing. Inductors with 1μm Co-Ta-Zr produced inductance values up to 60% higher than the air core inductors at frequencies up to 1.4 GHz.
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Lee, Duhyun, G. H. Jeong, J. H. Kim, Y. S. Kim, and S. J. Suh. "Micro-patterned NiFeMo Magnetoimpedance Multilayer for Magnetic Sensor Application." MRS Proceedings 906 (2005). http://dx.doi.org/10.1557/proc-0906-hh01-09.
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AbstractAs an alternative to the magnetoimpedance (MI) devices made from amorphous ribbon or wire, this study proposed a thin film type MI device composed with Ag conductive core and soft ferromagnetic NiFeMo sandwich layers. Obtained optimum sandwich structure was Ta 5 nm/ NiFeMo 300 nm/ Ta 5 nm/ Ag 900 nm/ Ta 5 nm/ NiFeMo 300 nm/ Ta 5 nm, and the width of Ag as 20 µm and the width of NiFeMo as 100 µm. It was patterned by using photolithography and lift-off process. The sandwich structure showed the maximum MI ratio about 40% at the 15 MHz. The impedance change was linear and nearly reversible at the external magnetic field region below the anisotropy field.
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Khitun, Alexander, Mingqiang Bao, Joo-Young Lee, Kang Wang, Dok Won Lee, and Shan Wang. "Spin Wave Based Logic Circuits." MRS Proceedings 998 (2007). http://dx.doi.org/10.1557/proc-998-j06-05.
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ABSTRACTWe investigate spin wave propagation and interference in conducting ferromagnetic nanostructures for potential application in spin wave based logic circuits. The novelty of this approach is that information transmission is accomplished without charge transfer. A bit of information is encoded into the phase of spin wave propagating in a nanometer thick ferromagnetic film. A set of “AND”, “NOR”, and “NOT” logic gates can be realized in one device structure by utilizing the effect of spin wave superposition. We present experimental data on spin wave transport in 100nm CoFe films at room temperature obtained by the propagation spin wave spectroscopy technique. Spin wave transport has been studied in the frequency range from 0.5 GHz to 6.0 GHz under different configurations of the external magnetic field. Both phase and amplitude of the spin wave signal are sensitive to the external magnetic field showing 60Deg/10G and 4dB/20G modulation rates, respectively. Potentially, spin wave based logic circuits may compete with traditional electron-based ones in terms of logic functionality and power consumption. The shortcomings of the spin wave based circuits are discussed.
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Harada, Keiichi, Hiroki Ishibashi, and Mineo Kogachi. "Defect Properties and Magnetism in B2-type CoFe Alloys." MRS Proceedings 753 (2002). http://dx.doi.org/10.1557/proc-753-bb5.28.
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ABSTRACTPoint defect properties have been studied for B2-type Co1-cFec alloys (0.4 ≤ c ≤ 0.6 ) by X-ray diffraction and density measurements. The lattice constant increases with increase in composition c and indicates a distinct change in the slope beyond c = 0.5. Further, it shows a decrease with increase in quenching temperature. The obtained vacancy concentration is very low for any composition and temperature concerned. Thus, it can be concluded that defect type in B2 CoFe is an antisite atom. The change in the lattice constant with quenching temperature can be related to the long-range order (LRO): it is well approximated by a linear form with respect to square of the LRO parameter. CoFe alloys in both B2 and higher temperature A2 phase regions show ferromagnetism. Observed results are discussed taking a correlation between the defect structure and the magnetic behavior into account.