Littérature scientifique sur le sujet « Spintronique THz »
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Articles de revues sur le sujet "Spintronique THz"
Garifullin, I. A. « The superconductor/ferromagnet proximity effect and its potential application in spintronics ». Uspekhi Fizicheskih Nauk 176, no 6 (2006) : 676. http://dx.doi.org/10.3367/ufnr.0176.200606l.0676.
Texte intégralThèses sur le sujet "Spintronique THz"
Kaushalya. « Ultrafast manipulation of magnetization using on-chip THz ». Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0173.
Texte intégralThe need for memory storage devices has skyrocketed over the last few decades especially after the development of the internet. This need has reached enormous heights in the past two years, soon after the pandemic due to COVID-19. Hard disk drives (HDDs) are known to have the potential to meet up with the high-density data storage demands. This thesis deals with one of the major challenges faced within the spintronic community to improve the speed and the energy consumption of memory devices.The speed of operation during the writing of a magnetic bit depends on the magnetization switching mechanism employed. The switching mechanism is itself dependent on the intrinsic magnetic properties of the sample and the externally induced excitation that drives the reversal of the magnetic bit 1. In this thesis, we will focus on the use of spin-orbit torque (SOT) excitations to drive the reversal, which is a relatively new but fast and energy-efficient approach in comparison with other state-of-the-art methods.The typical speed of magnetization reversal using SOTs is in the range of few nanoseconds, far slower than the picosecond-long switching that is possible with charge-based memory devices2. In fact, a record reversal speed with electrical pulses as short as ~200ps was reported by Garello et. al., 3 in 2011 using SOTs. This thesis reports further efforts to speed up the magnetization reversal by almost 2 orders of magnitude by exploiting such SOTs. To this aim, THz electrical pulses were generated via the use Auston photoconductive switches. We demonstrate that a single 6ps wide electrical pulse can induce a SOT to a 1nm thin Co ferromagnetic layer and result in a full magnetization reversal. A systematic study to understand SOTs in the picosecond time regime is also undertaken via using different magnetic nanostructures.In magnetic memory devices, a “read-head” is used to read the stored information in the device. Typically, in spintronic devices, giant magnetoresistance (GMR) or tunnel magnetoresistance (TMR) based read heads are used for such operations. In this thesis, we also report on the attempts of developing a GMR sensor working in the THz regime.To undertake the aforementioned studies, a pump-probe optical and optoelectrical experimental setup has also been built and a detailed report of the same is also provided in the thesis
Hawecker, Jacques. « Terahertz time resolved spectroscopy of Intersubband Polaritons and Spintronic Emitters ». Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS101.
Texte intégralThe terahertz (THz) domain provides a rich playground for many practical and fundamental applications, where the low energy of THz photons permits to probe novel light-matter interactions. This work investigates two recent and emerging scientific areas where ultrafast THz spectroscopy can be used as a probe of fundamental phenomena, as well as potentially enabling the conception of new THz sources. In the first case, ultrafast THz spintronics are studied where ultrafast excitations of spintronic heterojunctions result in efficient pulse generation. These structures consist of nanometer thick ferromagnetic - heavy metal junctions, where an optically generated spin-charge in the former is converted to a charge-current in the latter via the Inverse Spin Hall Effect. Beyond these metal-based junctions, ultrafast THz spintronics based on “quantum” materials is also investigated, where THz pulses are generated using quantum phenomena such as the Inverse Edelstein Effect in Topological Insulators, shown to be a promising research direction. The second subject area is focused on THz intersubband polaritons, quasi-particles that emerge from the strong light-matter coupling of a THz photonic cavity and an intersubband transition. Here we are interested in the bosonic nature of the intersubband polaritons, as a long-term aim of realizing a novel THz laser based on Bose-Einstein condensation. In this work, we investigate resonant narrowband pumping of a polariton branch and probe using spectrally broad THz pulses. This shows strong indications of nonlinear effects and potential signatures of scattering processes that could eventually lead to the demonstration of THz polaritonic gain. Finally, to support our work in the above subject areas, technological developments were made in existing THz sources. This included high power THz photoconductive switches using cavities, which permitted the first demonstrations of real time THz imaging with such devices, and high power THz quantum cascade lasers as narrowband laser pumps
Cadiz, Fabian. « Spin dependent electron transport in semiconductors due to the Pauli principle ». Palaiseau, Ecole polytechnique, 2015. https://theses.hal.science/tel-01174645/document.
Texte intégralThis thesis is concerned with transport of photoinjected minority spin-polarized electrons in doped semiconductors, as a function of both the density and the temperature of the injected electron gas. In p-GaAs thin films, charge and spin transport is investigated theoretically and experimentally by using a novel polarized microphotoluminescence (µPL) technique which consists in imaging the spatially-resolved PL intensity and polarization under a tightly-focused circularly-polarized CW laser excitation. Study of the experimental profiles at low concentration and under an applied electric field shows that the minority electron mobility is mainly determined by the electron temperature instead of the majority hole statistics, introducing a puzzling piece to the current understanding of scattering processes in semiconductors. At higher densities, this experimental technique has allowed us to explore a novel charge-spin coupling mechanism which modifies electron transport. Under degeneracy of the electron gas (high concentration, low temperature), a dip at the centre of the spin polarization profile appears with a polarization maximum at a distance of about r= 2 µm from the excitation. This counterintuitive result reveals that photoelectron diffusion depends on spin, as a direct consequence of the Pauli principle which causes in general a concentration dependence of the spin stiffness. This results in a novel spin filter effect in an homogeneous material. The other effects which may modify spin transport in a degenerate electron gas are thermoelectric spin currrents (spin Soret currents) and ambipolar coupling with holes. A comparison of the data with a numerical solution of the coupled diffusion equations reveals that ambipolar diffusion increases the steady-state photo-electron density at the centre and therefore the amplitude of the degeneracy-induced spin-dependent diffusion, while the contribution of the spin Soret current is negligible. Coulomb spin drag and bandgap renormalization are negligible due to electrostatic screening by the hole gas. It is expected for degeneracy to have larger effects in confined systems, such as quantum wells, where both the spin stiffness and the mobility can have a much strong spin dependence
Endichi, Asmaa. « Thin films based on Gadolinium applied to the magnetic refrigeration ». Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0150.
Texte intégralThe search for materials with a giant magnetocaloric effect in a massive state and at a temperature close to ambient temperature is of great interest and is mainly obtained by varying the composition of the materials. However, the first-order transition in these materials exhibits considerable thermal hysteresis, making them difficult to handle in applications for refrigerators operating cyclically. Much effort has been made in recent years to reduce this hysteresis, but the performance obtained with these massive materials does not meet the requirements of efficient magnetic refrigeration. Magnetocaloric materials have been largely unexplored on the nanoscale. However, nanostructuring is a well-known and used approach to disrupt the developed structure-property relationships, hence the interest in manufacturing new nanoscale materials. This will improve their magnetic and magnetocaloric characteristics by varying the size and shape. On the other hand, the magnetocaloric effect in magnetic thin layers is particularly interesting for micro-refrigeration. It is therefore important to study the magnetocaloric properties of materials in the form of thin layers in order to eliminate thermal hysteresis. In this sense, few studies have been done to show the potential of thin film materials for magnetic refrigeration and magnetic properties (saturation magnetization, variation of magnetic entropy and relative cooling ratio ...) measured so far limited remains. In this thesis project, we studied metallic gadolinium, which is the preferred choice as a magnetic refrigerant for most prototypes of active magnetic regenerator (AMR) in the form of a thin layer. The magnetocaloric (MCE) and electrocaloric (ECE) properties of the manufactured gadolinium films (Si / Ta / Gd (100 nm) / Pt (3nm)) are measured, in order to obtain more information on the physics behind the interesting electronic and magnetic properties of this material we demonstrate the magneto-caloric effect of the thin film Gd by measuring the electrical transport of the resistance. Thus, during this thesis, the electrical and especially magnetic behaviors of LaCr2Si2C and multiferroics TbMn2O5 are described using the ab-initio method, in order to broaden our understanding of the electronic, magnetic and therefore magnetocaloric characteristics of these compounds based on rare earth. The development of thin layers for magnetic refrigeration was carried out in the materials science research laboratory with the nanomagnetism and spin electronics team at the Jean Lamour Institute in Nancy and the theoretical calculations are made in the material laboratory condensed and interdisciplinary sciences at the Faculty of Sciences of Rabat
Duong, Quang ha. « Electrical control of the electron spin dynamics in [111]-oriented GaAs/AGaAs quantum wells ». Thesis, Toulouse, INSA, 2013. http://www.theses.fr/2013ISAT0006/document.
Texte intégralWe have studied the electron spin dynamics in <111>-oriented GaAs/AlGaAs quantum wells grown on <111>-substrate by time-resolved photoluminescence spectroscopy. By applying an external electric field about 50 kV/cm along growth direction, we observed the spectacular increase of electron spin which can attain values greater than 30 ns. This phenomenon comes from the electrical control of spin-orbit interaction in conduction band that make the Rashba term compensate exactly with the Dresselhaus term. The cancellation effect of these two terms results in the suppression of electron spin relaxation induced by D'yakonov-Perelmechanism which is dominant in undoped quantum wells and at the temperatures greater than 50K. The measurement under an external transverse magnetic field (Voigt configuration) demonstrates that the spin relaxation times in three spatial directions are also controlled simultaneously by electric field. The "total" control of electron spin relaxation can only be observed in <111>-oriented quantum wells. Finally, we also develop the model to interpret the experimental measurement of spin relaxation anisotropy depending on electric field in <111>-oriented quantum wells
Lesne, Edouard. « Non-Equilibrium Spin Accumulation Phenomena at the LaAlO3/SrTiO3(001) Quasi-Two-Dimensional Electron System ». Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066417/document.
Texte intégralWe investigated the generation, manipulation, and detection of non-equilibrium spin accumulation in the nonmagnetic LaAlO3/SrTiO3 (LAO/STO) oxide heterostructure, which is the host of a quasi-two-dimensional electron system (q2DES). In electrical tunneling spin injection experiments, we made use of the (three-terminal) Hanle effect to probe the magnitude of spin accumulation at Co/LAO/STO interfaces. We report on large amplification effects of the spin signal, ascribed to spin-conserving sequential tunneling processes via localized electronic states of enhanced spin lifetimes. A substantial modulation of the spin signal, by electrostatic field-effect, evidences the successful generation of spin accumulation inside the q2DES. We further resorted to ferromagnetic resonance experiments in a cavity to adiabatically pump a spin current from a permalloy layer toward the LAO/STO interface. We find that the generated spin current is converted into a sizeable planar charge current within the q2DES. This is attributed to an inverse Edelstein effect deriving from a Rashba-like spin-orbit interaction, both of which are efficiently modulated by electrostatic field-effect. Hence, our findings expand the general field of interest from planar charge transport to the exploration of spin-dependent phenomena in a prototypical nonmagnetic conducting oxide channel. Additionally, we have also demonstrated that the critical thickness threshold for the onset of a q2DES at LAO/STO interfaces can be reduced to a single unit cell of LAO when resorting to various metal capping layers. It opens up a new field of investigation to tentatively identify the potential mechanisms driving the formation of the q2DES
Lacoste, Bertrand. « Mastering the influence of thermal fluctuations on the magnetization switching dynamics of spintronic devices ». Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY039/document.
Texte intégralSpin-transfer torque magnetic random-access memory (STTRAM) are very promising non-volatile and enduring memories to replace charged-based RAM. However, in conventional in-plane or out-of-plane STTRAM technologies, the switching time is limited to about 10~ns because the reversal process is stochastic i.e. it is triggered by thermal fluctuations. In order to render the reversal deterministic and faster, an approach consists in adding to the magnetic tunnel junction (MTJ) stack another spin-polarizing layer whose magnetization is orthogonal to that of the MTJ reference layer. We particularly investigated the case where a perpendicular polarizer is added to an in-plane magnetized tunnel junction. The STT from the perpendicular polarizer initiates the reversal, but it also creates oscillations of the resistance between its two extremal values. This behavior is usually interesting to realize STT nano-oscillators (STO). In this thesis, the dynamics of the system comprising an in-plane free layer, an in-plane reference layer and a perpendicular polarizer is studied both experimentally and theoretically (analytically and by simulations) in the framework of the macrospin approximation. For a single layer free layer oscillating due to the STT of the perpendicular polarizer, an accurate description of the oscillations is presented, in which the anisotropy field, the applied field and the in-plane STT are treated as perturbations. In the particular case of a synthetic ferrimagnetic (SyF) free layer, analytical expressions of the critical currents and of the oscillations equation of motion are computed and compared to simulations. These results are used to determine the phase diagram of the complete system. The in-plane anisotropy field is found to play a dramatic role, which is confirmed by experimental data from real-time measurements on MgO-based nano-pillars. It is shown that the cell aspect ratio can be used to tune the relative influence of the STT from the in-plane reference layer and from the out-of-plane polarizer. This allows achieving well controlled sub-nanosecond switching in STTRAM
Huang, Tianxun. « A study about the behavior and mechanism of all-optical switching ». Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0054.
Texte intégralTo meet the future needs of high density, low power consumption, and fast rate of magnetic storage technology, it is one of the urgent tasks in the field of spintronics to develop a new method of magnetization manipulation with shorter magnetization reversal time and lower energy consumption. Ultrashort pulsed laser technology offers a new way to manipulate spins in femtosecond timescale, sparking great research interest in both academia and industry. Two methods of controlling magnetization by laser, all-optical helicity-dependent switching (AO-HDS) and all-optical helicity-independent switching (AO-HIS), are discovered recently and raise numerous discussion on their mechanisms, behaviors and applications. However, the origin of two phenomena is still largely debated, which will be the main task of this thesis. A Co/Pt multilayered stack exhibiting AO-HDS phenomenon is employed to study the mechanism of AO-HDS. The film is fabricated to a 10x10 um^2 magnetic square on a Hall bar and its switching behavior is observed optically and electrically at different timescale. The switching of this magnetic unit can be demonstrated with ten consecutive circularly polarized laser pulses. The spin dynamics of AO-HDS can be understood in terms of the magnetic domain thermal nucleation and domain wall propagation driven bythermal gradient. For the past years, AO-HIS has never been observed in other rare-earth transition-metal alloys except when the rare-earth is Gd. To study the speciality of Gd, a complete series of GdRCo (R represents Tb, Dy or Ho) alloys is grown and investigated, it is demonstrated that AO-HIS can be observed when the composition of R is as low as 1.5% near the compensation point of ferrimagnet. State diagrams describing the key parameters depending on the element concentrations and spin dynamics in various samples are studied, providing some suggestion on the origin of AO-HIS and its engineering application in the future
Verdierre, Gaétan. « Development of new material systems for the ferroelectric control of Rashba spin-orbit coupling and spin-charge interconversion ». Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP018.
Texte intégralWhile classical spintronics has traditionally relied on ferromagnetic metals as spin generators and spin detectors, spin-orbit effects now make it possible to efficiently generate and detect spin currents from charge currents in architectures free from ferromagnets.However, existing materials able to achieve this spin/charge interconversion do not possess the non-volatile character of ferromagnets required for non-volatile data storage and processing. In the work presented in this thesis, we tried to develop material systems in which it would be possible to combine the advantages of Rashba-type spin-orbit coupling (RSOC) for efficient interconversion between spin and charge currents with another family of ferroic systems, ferroelectrics. RSOC appears in systems with broken inversion symmetry, and is stronger in the presence of heavy elements. Ferroelectrics intrinsically break inversion symmetry and could thus harbour RSOC.As a bonus, switching the polarization of the ferroelectric with an electric field should switch the sign of the RSOC and thus the polarity with which the material would interconvert spin into charge via the Edelstein effect. In addition, ferroelectrics can accumulate or deplete very large carrier densities in adjacent materials and thus generate interfacial electric fields that would depends on the ferroelectric polarization direction. This would result in an interfacial RSOC that should also be tunable, allowing for a non-volatile electrical control of spin/charge interconversion.In the framework of this thesis, we investigated the growth and characterisation of two types of ferroelectric thin film heterostructures which should present switchable RSOC: (i) a single phase material, SrBiO₃, that we predicted to become ferroelectric with switchable RSOC at compressivestrain; (ii) an interface system combining the novel family of ferroelectrics, the wurtzites (Al,Sc)N, with BiSb, a topological insulator whose spin-charge interconversion properties could be modulated through the means of ferroelectricity
Talatchian, Philippe. « Bio-inspired computing leveraging the synchronization of magnetic nano-oscillators ». Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS008/document.
Texte intégralSpin-torque nano-oscillators are non-linear, nano-scale, low power consumption, tunable magnetic microwave oscillators which are promising candidates for building large networks of coupled oscillators. Those can be used as building blocks for neuromorphic hardware which requires high-density networks of neuron-like complex processing units coupled by tunable connections. The neuromorphic approach allows to overcome the limitation of nowadays computers and to reduce their energy consumption. Indeed, in order to perform cognitive tasks as voice recognition or image recognition, the brain is much more efficient in terms of energy consumption. Due to the large number of required neurons (100 billions), a neuromorphic chip requires very small oscillators such as spin-torque nano-oscillators to emulate neurons. Recently a first demonstration of neuromorphic computing with a single spin-torque nano-oscillator was established, allowing spoken digit recognition with state of the art performance. However, to realize more complex cognitive tasks, it is still necessary to demonstrate a very important property of neural networks: learning an iterative process through which a neural network can be trained using an initial fraction of the inputs and then adjusting internal parameters to improve its recognition or classification performance. One difficulty is that training networks of coupled nano-oscillators requires tuning the coupling between them. Here, through the high frequency tunability of spin-torque nano-oscillators, we demonstrate experimentally the learning ability of coupled nano-oscillators to classify spoken vowels with a recognition rate of 88%. To realize this classification task, we took inspiration from the synchronization of rhythmic activity of biological neurons and we leveraged the synchronization of spin-torque nano-oscillators to external microwave stimuli. The high experimental recognition rates stem from the weak-coupling regime and the high tunability of spin-torque nano-oscillators. Finally, in order to realize more difficult cognitive tasks requiring large neural networks, we show numerically that arrays of hundreds of spin-torque nano-oscillators can be designed with the constraints of standard nano-fabrication techniques