Добірка наукової літератури з теми "Opto-Spintronics"

We offer a perspective on the prospects of ultrafast spintronics and opto-magnetism as a pathway to high-performance, energy-efficient, and non-volatile embedded memory in digital integrated circuit applications. Conventional spintronic devices, such as spin-transfer-torque magnetic-resistive random-access memory (STT-MRAM) and spin–orbit torque MRAM, are promising due to their non-volatility, energy-efficiency, and high endurance. STT-MRAMs are now entering into the commercial market; however, they are limited in write speed to the nanosecond timescale. Improvement in the write speed of spintronic devices can significantly increase their usefulness as viable alternatives to the existing CMOS-based devices. In this article, we discuss recent studies that advance the field of ultrafast spintronics and opto-magnetism. An optimized ferromagnet–ferrimagnet exchange-coupled magnetic stack, which can serve as the free layer of a magnetic tunnel junction (MTJ), can be optically switched in as fast as ∼3 ps. Integration of ultrafast magnetic switching of a similar stack into an MTJ device has enabled electrical readout of the switched state using a relatively larger tunneling magnetoresistance ratio. Purely electronic ultrafast spin–orbit torque induced switching of a ferromagnet has been demonstrated using ∼6 ps long charge current pulses. We conclude our Perspective by discussing some of the challenges that remain to be addressed to accelerate ultrafast spintronics technologies toward practical implementation in high-performance digital information processing systems.

Spintronics represents a new paradigm for future electronics, photonics and information technology, which explores the spin degree of freedom of the electron for information storage, processing and transfer. Since 1990s, we have witnessed great success of metal-based spintronics that has revolutionized the mass data storage industry. There has also been an enormous push for semiconductor spintronics during the past three decades, with the aim to capitalize the past and current success of charge-based semiconductor technology and to make its spin counterpart the backbone of future spintronics just like semiconductors have done in today’s electronics/photonics. An exclusive advantage of semiconductor spintronics is its potential for opto-spintronics that will allow integration of spin-based information processing and storage with photon-based information transfer and communications. Unfortunately, progresses of semiconductor spintronics have so far been severely hampered by the failure to generate nearly fully spin-polarized charge carriers in semiconductors at and above room temperature (RT) at which today’s devices operate. In this work, we succeed to achieve conduction electron spin polarization exceeding 90% at RT in a semiconductor nanostructure, which remains steadily high even up to 110°C [1]. This represents the highest RT electron spin polarization ever reported in any semiconductor by any approach! This breakthrough is accomplished by a conceptually new approach of defect-engineered remote spin filtering and amplification of InAs quantum-dot (QD) electrons via an adjacent tunneling-coupled GaNAs quantum well acting as a spin filter. The extraordinary spin filtering effect in GaNAs is enabled by spin-dependent recombination via spin-polarized defects, i.e. grown-in Ga self-interstitials, which selectively deplete conduction electrons with an opposite spin orientation to that of the defect electron. In sharp contrast to the general trend of deteriorating spin polarization with increasing temperature seen in all other approaches of spin generation, our approach is gifted with an opposite temperature dependence up to RT thanks to a thermally accelerated remote spin-filtering effect as a result of thermally activated recombination via the defects [2]. We further show that the QD electron spin can be remotely manipulated by spin control in the adjacent spin filter, paving the way for remote spin encoding and writing of quantum memory as well as for remote spin control of spin-photon interfaces. This work demonstrates the feasibility to implement opto-spintronic functionality under practical device operation conditions in a semiconductor nanostructure system based on the mature III-V semiconductor technology commonly used for today’s optoelectronics and photonics. It could also pave the way for a range of potential spintronic and opto-spintronic applications exploiting the state-of-the-art GaAs technology platform, such as spin-LEDs, spin lasers, spin-polarized single-photon sources, quantum spin-photon interfaces, spin qubits, etc. References [1] Y.Q. Huang, V. Polojärvi, S. Hiura, P. Höjer, A. Aho, R. Isoaho, T. Hakkarainen, M. Guina, S. Sato, J. Takayama, A. Murayama, I.A. Buyanova and W.M. Chen, Nature Photonics 15, 475 (2021). [2] Y.Q. Huang, Y. Puttisong, P. Höjer, A. Aho, R. Isoaho, T. Hakkarainen, M. Guina, I.A. Buyanova and W.M. Chen, unpublished

Spin-orbit interactions (SOI), describing the transfer of a spin degree of freedom to an orbital angular momentum (OAM), have been widely explored in recent opto-acoustic studies for applications mainly in spintronics and for topological insulators [1]. We report the observation of SOI by Brillouin scattering in an optical nanofiber. Specifically, we describe the transfer of a spin degree of freedom from light incident to the nanofiber to an acoustic vortex with a topological charge of order 2 in the form of OAM. Coupled with the phase matching condition for the energy conservation during Brillouin scattering, it results in a backscattered wave with a spin opposite to the incident wave. This observation allows considering applications of opto-acoustic Brillouin memory based on polarization conversion through a SOI [2].

Investigation of the interaction of ultrashort laser pulses with magnetically ordered materials has become a fascinating research topic in modern magnetism. Especially, the control of magnetic order by sub-ps laser pulses has become a fundamentally important topic with a high potential for future spintronics applications. This paper will review the recent success in optically controlling the magnetic interactions in carrier-density-controlled ferromagnetic semiconductor EuO doped with Gd ions. When the Gd concentration is low, the magnitude of the magnetic interaction is enhanced by the irradiation of ultrashort laser pulses, whereas it is attenuated when the Gd concentration is high. In ferromagnetic Eu1−xGdxO, we thereby demonstrate the strengthening as well as the weakening of the magnetic interaction by 10% and within 3 ps by optically controlling the magnetic exchange interaction. This principle—ultrafast optical control of magnetic interaction—can be applied to future ultrafast opto-spintronics.

III-Nitride semiconductors are the materials of choice for state-of-the-art opto-electronic and high-power electronic applications. Through the incorporation of magnetic ions, like transition metals and rare-earths, III-Nitrides have further extended their applicability to spintronic devices. However, in most III-Nitrides the low solubility of the magnetic ions leads to the formation of secondary phases that are often responsible for the observed magnetic behavior of the layers. The present review summarizes the research dedicated to the understanding of the basic properties, from the fabrication to the performance, of III-Nitride-based phase-separated magnetic systems containing embedded magnetic nanostructures as suitable candidates for spintronics applications.

Monolayers of transition metal dichalcogenides (TMDCs), due to their tunable properties, have shown immense promise in applications such as optoelectronics, flexible electronics, spintronics and energy harvesting. Defect engineering has emerged as a facile tool to tune the properties of monolayer TMDCs making them more potent for these applications. While a high propensity of defects is useful for certain applications like catalysis, many other applications benefit from low defect densities. Thus, understanding the nature of these defects as well as finding quick throughput techniques to characterize them have become critical. Additionally, although several efforts have focused on creation/healing of defects, these processes are still premature and not well understood. In this talk, we will discuss defect engineering in large area epitaxial monolayer MoS2 thin films. We will outline in-situ approaches for fabrication/healing of defects. We will also demonstrate a quick throughput technique to characterize defect densities in these thin films. We envision the ability to modulate defect densities (create/heal) in a controllable fashion in these materials can open-up an additional knob to tune the opto-electronic properties of these materials thus making them more marketable for applications in opto-electronics, photonics, energy harvesting and beyond.

La demande de stockage de données a connu une croissance exponentielle, alimentée par la dépendance croissante du monde à l'égard de l'information numérique. Cette croissance a catalysé le développement de technologies plus rapides et plus éco-énergétiques. Ce développement coïncide avec les objectifs de la spintronique, un domaine visant à réduire la consommation d'énergie dans le stockage de données magnétiques en explorant des alternatives basées sur le spin. En conséquence, des recherches approfondies ont été consacrées à la manipulation de la magnétisation (c'est-à-dire les spins), qui est au cœur de la spintronique, formant un programme de recherche substantiel et durable. La vitesse et l'efficacité de cette manipulation dépendent des méthodes d'écriture utilisées et des propriétés des matériaux magnétiques impliqués, nécessitant ainsi une compréhension approfondie des mécanismes de manipulation sous-jacents. Parmi les différentes techniques d'écriture, l'utilisation d'impulsions laser ultracourtes (femtosecondes) a attiré une attention considérable en raison de sa capacité à exciter rapidement la magnétisation à l'échelle femtoseconde. Une seule impulsion laser femtoseconde a été démontrée pour induire une inversion complète de la magnétisation dans les matériaux magnétiques, un phénomène connu sous le nom de commutation optique complète indépendante de l'hélicité (AO-HIS). Cependant, le mécanisme sous-jacent et les critères de l'AO-HIS restent incomplètement compris. De plus, depuis le premier rapport de l'AO-HIS, cet effet a principalement été observé dans un groupe spécifique de matériaux magnétiques présentant une anisotropie magnétique perpendiculaire. De plus amples efforts et études sont nécessaires pour élargir l'applicabilité de l'AO-HIS. Pour atteindre cet objectif, cette thèse se concentre sur l'étude de l'AO-HIS dans une gamme de matériaux ferrimagnétiques et ferromagnétiques caractérisés par une anisotropie magnétique dans le plan. Nous utilisons des impulsions laser femtosecondes pour induire l'inversion de la magnétisation dans ces matériaux. De plus, nous entreprenons une exploration systématique visant à comprendre l'AO-HIS en modifiant les propriétés magnétiques des hétérostructures magnétiques. Cette manipulation comprend la variation des concentrations d'alliage, des températures de Curie, des épaisseurs et du type de couches magnétiques. Nous considérons nos résultats comme cruciaux d'un point de vue fondamental. Les résultats expérimentaux de cette thèse sont présentés dans trois chapitres (Chapitres 4 à 6). Dans le Chapitre 4, nous avons largement discuté de la commutation optique complète déterministe observée dans une large gamme de concentrations d'alliage et d'épaisseurs dans les films minces de GdCo magnétisés dans le plan, en utilisant un système de microscopie à effet Kerr magnéto-optique basé sur un laser. Les Chapitres 5 et 6 explorent le processus de transition des multiples aux inversions uniques de la magnétisation dans les matériaux ferromagnétiques magnétisés dans le plan, induit par des impulsions de courant de spin optiquement générées
The demand for data storage has experienced exponential growth, driven by the world's increasing reliance on digital information. This growth has catalyzed the development of faster and more energy-efficient technologies. This development coincides with the objectives of spintronics, a field aimed at reducing energy consumption in magnetic data storage by exploring spin-based alternatives. As a result, extensive research has been dedicated to the manipulation of magnetization (i.e., spins), which lies at the heart of spintronics, forming a substantial and enduring research agenda. The speed and efficiency of this manipulation depend on the methods of writing employed and the properties of the magnetic materials involved, thus requiring a comprehensive understanding of the underlying manipulation mechanisms. Among the various writing techniques, the utilization of ultrashort (femtosecond) laser pulses has gained considerable attention for its capability to rapidly excite magnetization on the femtosecond timescale. A single femtosecond laser pulse has been demonstrated to induce full magnetization reversal in magnetic materials, a phenomenon known as all-optical helicity-independent switching (AO-HIS). However, the underlying mechanism and criteria for the AO-HIS remain incompletely understood. Moreover, since the initial report of AO-HIS, this effect has mainly been observed in a specific group of magnetic materials exhibiting perpendicular magnetic anisotropy. Further endeavors and studies are necessary to broaden the applicability of AO-HIS. In pursuit of this goal, this thesis focuses on investigating AO-HIS in a range of ferrimagnetic and ferromagnetic materials characterized by in-plane magnetic anisotropy. We employ femtosecond laser pulses to drive magnetization reversal in these materials. Furthermore, we undertake a systematic exploration aimed at comprehending AO-HIS by altering the magnetic properties of magnetic heterostructures. This manipulation includes varying alloy concentrations, Curie temperatures, thicknesses, and the type of magnetic layers. We consider our findings crucial from a fundamental perspective. The experimental findings of this thesis are presented in three chapters (Chapters 4 to 6). In Chapter 4, we extensively discussed the deterministic AO-HIS observed in a broad range of alloy concentrations and thicknesses in in-plane magnetized GdCo thin films, utilizing a laser-based magneto-optic Kerr effect microscopy system. Chapters 5 and 6 delve into the recipe of transitioning from multiple to single magnetization reversals in in-plane magnetized ferromagnetic materials, induced by optically generated spin current pulses