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Teses / dissertações sobre o assunto "Spintronique ultra-Rapide"
Kaushalya. "Ultrafast manipulation of magnetization using on-chip THz". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0173.
Texto completo da fonteThe 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
Peng, Yi. "Single laser pulse switching in RE-based multilayers without Gd". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0297.
Texto completo da fonteThe emerging field of ultrafast spin electronics integrates the ideas and concepts of magneto-optics and opto-magnetism with spin transport phenomena, supplemented with the possibilities offered by photonics for ultrafast low-dissipative manipulation and transport of information. The discovery of all-optical ultra-fast deterministic magnetization switching has opened up new possibilities for manipulating magnetization in devices using femtosecond laser pulses. HI-AOS is predominantly observed in Gadolinium-based Rare Earth (RE) / Transition Metals (TM) ferrimagnetic alloys or multilayers. Notably, it has recently been witnessed in materials without Gadolinium, such as the ferrimagnet Mn2RuxGa and the ferrimagnetic multilayer [Tb/Co]N. In this work, we tried to find new materials that can show single-shot helicity-independent all-optical switching (HI-AOS) and to understand the switching behavior, fundamental mechanism, and switching process in different materials and structures. Therefore, three main parts of work have been done in this thesis:• Study the CoLu alloy, where Lu has the same properties as Gd with small spin-orbit coupling (L=0). Perpendicular magnetic anisotropy can be obtained in 3 nm of Co100-xLux alloy with x varies between 22% and 42%. Besides, single-shot switching measurements in full film and 3 μm dots array show that nodeterministic switching of the magnetization can be observed. The results can be attributed to the low magnetization and, consequently, too-small angular momentum carried by the Lu element by atomistic simulations. • Single-shot switching in [RE/TM]N multilayers, where the RE layer could be rare-earth metal with larger spin-orbit coupling such as Tb and Dy, and their alloy with transition metals. Starting with [Tb/Co]5 and [Tb/Fe]4 multilayers, the single-shot switching has been extended to various multilayers, bilayers, and trilayers, making it a general phenomenon in Tb- and Dy-based multilayers, which have sperimagnetic properties coupled with transient metals. Interestingly, a complex structure of rings of opposite magnetization directions has been observed at high fluence. According to the pump-probe measurements,We tried to explain the switching mechanism and ring structures, which could be an in-plane reorientation precession mechanism. • Single-shot switching in [Co/Ho]N multilayers, which is a novel material system with the expectation of higher spin-orbit coupling compared to Tb and Dy. Surprisingly, even though the spin-orbit coupling in Ho ( as it is in Tb and Dy) is larger than that of in Gd, which should increase the dissipation of angular momentum to the lattice, the pulse duration/fluence state diagram is close to the Gd-based systems. Studying this new system could help bridge the single pulse reversal processes observed, on the one hand, in Gd-based, on the other hand, in the Tb or Dy-based heterostructures
Fan, Xiaofei. "Contrôle ultrarapide de l'aimantation dans des hétérostructures à base de VO₂". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0271.
Texto completo da fonte(1) We have investigated the phase transition in ultrathin amorphous VO₂ and its physical mechanism: We have successfully prepared ultrathin (nano-scale) amorphous VO₂ films with significant phase transition by magnetron sputtering and demonstrated the phase transition of amorphous VO₂ - EGT. In addition, we quantitatively modeled the phase transition of amorphous VO₂ and classified different thicknesses of VO₂ into "strong system" (>5 nm) and "fragile system" (0-2 nm). For the strong system, the material properties are less affected by temperature, and the Arrhenius model is used to describe the electron transport of VO₂ phase transition. While for the fragile system, the material properties are more affected by temperature fluctuations, and the Vogel-Tammann-Fulcher model can be used for analysis. The results demonstrate the phase transition mechanism of amorphous materials and provide a new idea for understanding phase transition. In addition, this direct method of growing ultrathin VO₂ using magnetron sputtering is convenient and fast, and it can be grown in the same batch with other materials within the heterostructure, which is expected to promote the application of phase transition materials in practical devices.(2) We explored a method to dynamically regulate the interlayer exchange coupling by phase transition: we introduced the VO₂ into the ferromagnetic/nonmagneticspacer/ferromagnetic heterostructure, and successfully realized the reversible transformation of the antiferromagnetic coupling and ferromagnetic coupling through regulating conduction electrons by MIT of VO₂. At the same time, from the analysis of the change of magnetic properties, we clarify that the IEC induced by VO₂ in different electronic states is dominated by the RKKY and spin dependent tunneling. Furthermore, we fully investigate the physical root behind the regulation of IEC by the VO₂, and reveal the regulation mechanism of the interface spin effect by the regulation of electronic states of non-magnetic spacer. This part of the work proposes a novel approach to the dynamic regulation of IEC, which provides new ideas for the application of IEC in spintronic devices.(3) We study the dynamic regulation of spin-polarized hot electron transport by phase transition: In a ferrimagnetic/nonmagnetic diffusion channel/ferromagnetic heterostructure, we introduce VO₂ into the diffusion channel to control the electrical properties of the channel by MIT, and then dynamically regulate the transport of spin-polarized hot electrons generated by the ultrafast demagnetization of GdCo. By regulating the on/off of hot electrons in the channel, we achieve dynamic regulation of the magnetization of adjacent ferromagnetic layers. Meanwhile, with the optical property changes introduced by VO₂, we have successfully achieved the switching of the magnetization of ferromagnetic materials without AOS in ferrimagnetism excited by a single-pulse femtosecond laser. Furthermore, we have verified and analyzed the mechanism of this ultrafast modulation. In this work, we use the phase transition material VO₂ as a diffusion channel with controllable electrical properties to control the hot electron transport through MIT. The results show that the non-magnetic materials play an important role in various types of heterostructures
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.
Texto completo da fonteTo 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
Chirac, Théophile. "New spintronic components based on antiferromagnetic materials". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS482.
Texto completo da fonteCurrent magnetic memory devices are reaching their physical limits in terms of stability, speed and power consumption as the race to miniaturization intensifies. The emergent research field of spintronics studies the collective behavior of spins in matter and their interplay at interfaces, to find new avenues in terms of materials, architectures and stimulation sources. A particularly promising group of materials are the antiferromagnets. These abundant magnetically ordered materials are naturally stable, robust, ultra-fast and compatible with insulator electronics. Indeed, most transition metal oxide compounds are antiferromagnetic insulators, have resonance in the terahertz range and flop fields of tens of teslas. They can also be semi-metals, metals, semiconductors, superconductors or multiferroics. This thesis focuses on two antiferromagnets: nickel oxide (NiO) and bismuth ferrite (BiFeO₃). NiO is the archetypical antiferromagnet at ambient temperature with a simple crystalline structure. Using dynamical atomistic simulations, I show that this compound can be the elemental brick of a three state memory device controlled by currently available pulses of spin currents, with a picosecond response time. The simulations also explain the formation of chiral structures in BiFeO₃, a ferroelectric antiferromagnet with magnetoelectric coupling between the two orders. In a second part, antiferromagnetic domains in BiFeO₃ are experimentally observed using second harmonic generation of light, with a sub-micron spatial resolution. Antiferromagnetic domains of BiFeO₃ are then excited by an intense femtosecond laser pulse, and the dynamics of the two coupled orders (antiferromagnetism and ferroelectricity) is studied with a sub-picosecond time resolution. Finally, the injection of spin current in an antiferromagnet such as BiFeO₃ or NiO is envisioned by characterizing the spin bursts generated by ultrafast laser-induced demagnetization of adjacent ferromagnetic layers
Zhao, Fan. "Recombinaison dépendante du spin dans les semiconducteurs nitrures dilués". Thesis, Toulouse, INSA, 2010. http://www.theses.fr/2010ISAT0013/document.
Texto completo da fonteThis thesis work is a contribution to the investigation of the spin properties of semiconductors by photoluminescence and photoconductivity spectroscopy with the aim of future applications in the spintronic field. We have studied the conduction band electron spin properties of dilute nitride semiconductors in epilayers and quantum wells (GaAsN, GaAsN/GaAs). In particular, we have investigated the spin dependent recombination of conduction band electrons on deep paramagnetic centers induced by the introduction of nitrogen into GaAs. We have also evidenced the “spin filtering” effect made possible by this spin dependent recombination mechanism. More precisely, we have carried out a systematic study of the spin filtering effect as a function of the nitrogen concentration, excitation power, external magnetic field and, for the hetero-structures, as well as a function of the quantum well thickness. The chemical origin of the deep paramagnetic centers has been also determined by optically detected magnetic resonance (ODMR). We have completed these all-optical studies on the spin dependent recombination by photoconductivity experiments in order to demonstrate a “proof of concept” system for spintronic applications. We have shown that the photoconductivity in dilute nitride semiconductors can be controlled by the polarization of the incident light: an electrical detector of the light polarization has therefore been built. These results have been as well modeled thanks to a rate equation system able to reproduced both the photoluminescence and photoconductivity experimental results
Guillemard, Charles. "Half-metal magnets Heusler compounds for spintronics". Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0110.
Texto completo da fonteImprovements in thin film elaboration methods and a deeper understanding of condensed matter physics have led to new exciting phenomena in spin electronics (spintronics). In particular, magnetization reversal by spin-orbit and spin-transfer torque as well as the development of spin waves based devices have placed the Gilbert magnetic damping coefficient as a key parameter for future data storage and information processing technologies. The prediction of ultralow magnetic damping in Co2MnZ Heusler half-metal magnets is explored in this study and the damping response is shown to be linked to the underlying electronic structure. By substitution of the Z element in high quality Co2MnZ (Z=Al, Si, Ga, Ge, Sn and Sb) epitaxial thin films grown by molecular beam epitaxy, electronic properties such as the minority-spin band gap, Fermi energy position in the band gap, and spin polarization can be tuned and the consequences for magnetization dynamics analyzed. Experimental results allow us to directly explore the interplay of spin polarization, spin gap and Fermi energy position, with the magnetic damping obtained in these films (together with predictions from ab initio calculations). The ultralow magnetic damping coefficients measured in the range from 4.1 x10-4 to 9 x10-4 for Co2MnSi, Co2MnGe, Co2MnSn and Co2MnSb are the lowest values ever reported in conductive layers and offer a clear experimental demonstration of theoretical predictions on half metal magnetic Heusler compounds. Then, the relation between the Gilbert damping and the ultrafast demagnetization time in quaternary Co2MnSixAl1-x compounds with a tunable spin polarization is analyzed. This way, it is possible to confront theoretical models unifying those two quantities that live in different timescales. Finally, structural and magnetic properties of Mn3Ga/Co2YZ Heusler superlattices are investigated in order to combine ultralow Gilbert damping coefficient, minority spin band gap and perpendicularly magnetized heterostructures, another requirement for low energy consumption devices. Through the present work, we aim to prove that Heusler compounds provide an excellent playground to study fundamental magnetism and offer a pathway for future materials design