Ferromagnetism in dilute magnetic semiconductors and new materials for spintronics

Spintronics materials may be classified under concentrated magnetic semiconductors, semimetals and half-metals, semimagnetic semiconductors, and dilute magnetic semiconductors (DMS). The nature of ferromagnetism, that occurs in p-type DMS with an increase in the transition metal content, is governed by the proposed kinematic exchange involving the kinetic energy gain of the heavy hole carriers caused by their hybridization with 3d electrons of impurities. The synthesis of DMS (In,Mn)Sb is proposed on the basis of hint at its T_C from kinematic mechanism. The effect of the dimensionality-driven T_C increase is derived for spintronics materials such as delta-doped DMS (DDMS) and DMS heterostructures. The state-of-the-art in the field of synthesis and research of “new” DMS with announced “high T_C” is also outlined with particular attention to chalcopyrite-based systems.     

Multiferroics: Promising materials for microelectronics,spintronics, and sensor technique

Possible areas of application of magnetoelectric materials and multiferroics in microelectronics, spintronics, and sensor technique are considered. Criteria of practical applicability of such materials are formulated and examples of magnetoelectric materials satisfying these criteria are given.     

新型光学材料发展综述

新型光学材料是指光电数码及信息产品所应用的技术含量高、制作难度大、光学性能优越的光学材料,一般是指镧系光学玻璃、环保系列光学玻璃、低熔点及磷酸盐光学玻璃等。目前我国光学材料的研究开发水平与国外发达国家相比还有一定的差距,特别是与日本和德国等国际知名光学材料生产厂家相比,无论从光学玻璃品种还是生产工艺及设备都存在着明显的差距。目前我国光学材料行业仍以生产传统的光学玻璃为主,一些新型材料需从国外进口,不能完全满足我国高科技发展的需要。在光学材料方面,我国急待需要进行技术研究和技术创新工作,即开发新型的光学材料,研究先进的制造工艺以及测试技术,尽快形成我国的产业化规模生产。     

纳米级自旋电子学材料取得重要进展

因为纳米级的自旋电子学器件需要在纳米尺度上仍能在较高温度下保持优异性能的高自旋极化率材料，故与半导体相容的半金属铁磁体近来受到高度重视．文章介绍作者在这个方向上研究工作的最新重要进展：通过大规模系统的高精度第一原理计算，作者发现三个3d过渡金属硫系化合物的闪锌矿相具有优异的半金属铁磁性，并且其结构性能适合做成具有足够厚度的薄膜或层状材料，便于应用于纳米级自旋电子学器件。     

有机自旋电子学

文章介绍了有机半导体同自旋电子学相结合的新学科——有机自旋电子学. 着重讨论以下三个方面问题: 有机半导体特别是有机共轭聚合物特性及其载流子性质; 自旋电子学研究热点; 有机自旋电子学研究进展.     

Manganese-doped CdGeAs2, ZnGeAs2 and ZnSiAs2 chalcopyrites: New materials for spintronics

New diluted magnetic semiconductors (CdGeAs₂:Mn, ZnGeAs₂: Mn, and ZnSiAs₂: Mn chalcopyrites) were synthesized. Magnetization M, electrical resistivity, magnetoresistance, and the Hall effect of these compositions were examined. Although the M(T) curves are complicated, they are similar in shape, for which the concentration and mobility of the charge bearers. Their Curie points are higher than 300 K, the highest in systems of the A ^II B ^IV C ₂ ^V : Mn type.     

Carbon-based spintronics

Carbon-based spintronics refers mainly to the spin injection and transport in carbon materials including carbon nanotubes,graphene,fullerene,and organic materials.In the last decade,extraordinary development has been achieved for carbon-based spintronics,and the spin transport has been studied in both local and nonlocal spin valve devices.A series of theoretical and experimental studies have been done to reveal the spin relaxation mechanisms and spin transport properties in carbon materials,mostly for graphene and carbon nanotubes.In this article,we provide a brief review on spin injection and transport in graphene,carbon nanotubes,fullerene and organic thin films.     

Thin-film ferromagnetic composite material for spintronics

The results of a study of the magnetic and other parameters of thin-film EuO:Fe composites, which really meet the requirements imposed on the use of them as spin injectors in the developed semiconductor spin-electronic structures capable of operating under normal conditions at room temperatures, are reported.     

Progress in spintronics

The discovery of the giant magnetoresistance (GMR) by Peter Grünberg and Albert Fert in 1988, which was awarded with the Nobel Prize for Physics in 2007, initiated an upsurge of experimental and theoretical investigations on spin dependent transport phenomena. Since then, spin valves have been introduced, switching via spin torque was proposed and confirmed, the tunneling magneto-resistance effect has matured to marketability, and magnetic domain walls and their propagation are being developed for memory storage devices with enhanced density. This field, which embraces spin-structures and spin-transport on the nanoscale, was coined spin electronics or short spintronics. A brief overview on the development of spintronics from the early discovery of the GMR effect to the present activities is provided.     

Manganese-doped CdGeAs2, ZnGeAs2 and ZnSiAs2 chalcopyrites: A new materials for spintronics

Based on Mn-doped chalcopyrites CdGeAs₂, ZnGeAs₂ and ZnSiAs₂ the new dilute magnetic semiconductors with p-type conductivity were produced. Magnetization, electrical resistivity, magnetoresistance and Hall effect of mentioned compositions were studied. Their curves of temperature dependence of magnetization have the similar form in spite of complicated character, for which the concentration and mobility of the charge carriers are responsible. Thus, for T<15 K, these curves are characteristic for superparamagnetics and for T>15 K for a frustrated ferromagnetics. In compounds with Zn these two states dilute by spinglass-like state. This specific feature is assigned to an attraction of Mn ions occupying neighboring sites and to the competition between the carrier-mediated exchange and superexchange interactions. Curie temperatures of these compounds are above room temperature. These are the highest Curie temperatures in the A^IIB^IVC^V₂:Mn systems.     

Hybrid ferromagnetic/semiconductor heterostructures for spintronics

Heterostructures that integrate conventional semiconductors with ferromagnetic semiconductors and ferromagnetic metals are important for developing a framework for semiconductor spintronics. We describe recent efforts to study ‘hybrid’ ferromagnetic/semiconductor heterostructures that combine conventional III-V and II-VI semiconductors with the ferromagnetic semiconductor (Ga,Mn)As and the ferromagnetic metal MnAs. We focus on the characteristics of two novel classes of heterostructures: (a) (Ga,Mn)As/AlAs/MnAs magnetic tunnel junctions (MTJs) that provide an all-electrical scheme for probing spin injection from metals into GaAs and (b) n-ZnSe/(Ga,Mn)As heterojunction diodes that surprisingly exhibit a magnetically-driven photoconductivity.     

Nanojunctions as logic operators for the spintronics

We propose two all-electrical nanodevices where the spin properties of an incoming electron are modified by the spin-orbit interaction (SOI), resulting in a transformation of the qubit state carried by the spin. Our proposal is essentially based on nanojunctions made of crossing quantum wires patterned in a two dimensional electron gas where the Rashba SOI is present. We investigate in detail the spin precession of one electron traveling in the proposed nanodevices. The nanojunctions acts as spin filters or ballistic spin rotators whose properties can be varied by tuning the strength of the SOI, by changing the geometry of the junctions. Two different basic mechanism in order to obtain in plane or out of the plane rotations are discussed. We show that, starting from the spin rotators, a large class of unitary transformations can be attained with one or more nanojunctions in series. By choosing appropriate parameters the spin transformations can be made unitary, which corresponds to lossless operators.     

Perspectives of antiferromagnetic spintronics

Antiferromagnets are promising for future spintronic applications owing to their advantageous properties: They are magnetically ordered, but neighboring magnetic moments point in opposite directions, which results in zero net magnetization. This means antiferromagnets produce no stray fields and are insensitive to external magnetic field perturbations. Furthermore, they show intrinsic high frequency dynamics, exhibit considerable spin–orbit and magneto-transport effects. Over the past decade, it has been realized that antiferromagnets have more to offer than just being utilized as passive components in exchange bias applications. This development resulted in a paradigm shift, which opens the pathway to novel concepts using antiferromagnets for spin-based technologies and applications. This article gives a broad perspective on antiferromagnetic spintronics. In particular, the manipulation and detection of antiferromagnetic states by spintronics effects, as well as spin transport and dynamics in antiferromagnetic materials will be discussed. We will also outline current challenges and future research directions in this emerging field.     

Spin gapless semiconductor like Ti2MnAl film as a new candidate for spintronics application

A novel Heusler ferrimagnet Ti₂MnAl film has been grown on Si(001) substrate using magnetron sputtering. Characteristics of its magnetic and transport properties reveal the spin‐gapless‐semiconductor (SGS) nature of the stoichiometric Ti₂MnAl, in agreement with theoretical prediction. The as‐grown SGS‐like Ti₂MnAl film demonstrated high Curie temperature, nearly compensated ferrimagnetic properties with small coercivity and low magnetization. It also showed semiconductor‐like behavior at room temperature allowing good compatibility with commercial Si‐based semiconductor. In this regards, Ti₂MnAl film is a potential candidate material for spintronics application, especially for the minimization of energy consumption of device. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Semiconductor heterostructures for spintronics and quantum information

A selection of optical experiments is presented, demonstrating the utility of semiconductors in two novel areas of research: spintronics and quantum information. First we show examples of spin manipulation in semiconductor quantum wells. The light is used to generate a spin polarization and to detect it. Next we discuss application of optical methods in studies of carrier-induced ferromagnetism in quantum wells. Finally, we present examples of single quantum dot spectroscopy related to perspectives of application of quantum dots in quantum information, and, in particular, the use of photon correlation measurements as a tool to study the quantum dot excitation mechanisms. To cite this article: J.A. Gaj et al., C. R. Physique 8 (2007).     

Rare-earth doped III-nitride semiconductors for semiconductor spintronics

InGaGdN layers and InGaGdN/GaN superlattice (SL) structures were grown by plasma-assisted molecular beam epitaxy. InGaGdN layers exhibited photoluminescence emission at room temperature and its peak wavelength was red-shifted with the increase of In composition. Clear hysteresis and saturation were observed in the magnetization versus magnetic field curves at room temperature for the InGaGdN layers. Si co-doping into InGaGdN layers increased the electron carrier concentration and enhanced the magnetization. In the InGaGdN/GaN SL samples, enhanced magnetization was also observed. Si doping into wide bandgap GaN layers in these SL structures further increased the magnetization, where InGaGdN layers were not doped with Si. All these results can be understood with the carrier-mediated ferromagnetism.     

自旋电子学研究与进展

自旋电子学是最近几年在凝聚态物理中发展起来的新学科分支,它研究在固体中自旋自由度的有效控制和操纵,在金属和半导体中自旋极化、自旋动力学、自旋极化的输运和自旋电子检测.由于它在信息存储方面的重大应用前景,受到学术界和工业界的高度重视.文章扼要地介绍了自旋电子学发展的历程和发展中的最重要的发现.最近几年,最奇特的发现和最重要的应用莫过于巨磁电阻,薄膜领域纳米技术的迅速发展使巨磁电阻的应用变成可能.作为磁记录头它已使硬磁盘的记录密度提高到170Gbit/in2.动态随机存储器MRAM的研究已实现16Mbit的存储密度.     

Progress in organic spintronics

Recent progress in organic spintronics is given an informative overview, covering spin injection, detection, and trans-port in organic spin valve devices, and the magnetic field effect in organic semiconductors （OSCs）. In particular, we focus on our own recent work in spin injection and the organic magnetic field effect （OMFE）.