磁电子学器件应用原理

本文介绍几种重要的磁电子器件的基本结构和工作原理,包括巨磁电阻与隧穿磁电阻传感器、巨磁电阻隔离器、巨磁电阻与隧穿磁电阻硬盘读出磁头、磁电阻随机存取存储器、自旋转移磁化反转与微波振荡器。自旋晶体管作为未来磁电子学或自旋电子学时代的基本元素,目前大都还处在概念型阶段,本文也将对几种自旋晶体管的大致原理作简要介绍。     

自旋输运和巨磁电阻--自旋电子学的物理基础之一

介绍磁性纳米结构和锰氧化物中电子的自旋极化输运和巨磁电阻效应，它们是新近发展的自旋电子学的物理基础之一．着重讨论的是以下三方面的基本物理图像：磁多层结构的巨磁电阻，铁磁隧道结的隧穿磁电阻，掺杂锰氧化物的庞磁电阻效应．     

第五讲 自旋极化输运及隧道巨磁电阻效应

简要回顾了利用量子隧道效应测定铁磁金属传导电子自旋极化率的研究历史，综述了自旋极化电子隧穿产应导致的“铁磁金属／非磁绝缘体／铁磁金属”三层平面型隧道结中的巨磁电阻效应以及“铁磁金属／非磁绝缘体”颗粒膜系统中的隧穿类型巨磁电阻效应的研究进展。     

磁电子学中的若干问题

本文综述了自旋极化输运过程中巡游电子的自旋极化、自旋相关的散射及自旋弛豫等三方面的内容；全面总结了铁磁金属的磁电阻效应（ＡＭＲ）、磁性金属多层膜和颗粒膜的巨磁电阻效应（ＧＭＲ）、氧化物铁磁体的特大磁电阻效应（ＣＭＲ）以及磁隧道结的巨大隧道电阻效应（ＴＭＲ）研究中具有代表性的实验结果及理论模型；简单介绍了新生的磁电子器件—磁电阻型随机存取存储器（ＭＲＡＭ）和全金属自旋晶体管的工作原理和工作过程。     

自旋电子学材料、物理和器件设计原理的研究进展

文章介绍了作者所在实验室在巨磁电阻(GMR)、隧穿磁电阻(TMR)、庞磁电阻(CMR)和反铁磁钉扎薄膜材料以及单晶金属氧化物、高自旋极化率材料、P-N异质结和纳米环磁随机存储器原理型演示器件设计等研究方面取得的一些重要研究成果和进展.例如:在Al-O势垒磁性隧道结材料体系里,获得室温磁电阻超过80%的国际最好结果;获得两种高性能层状反铁磁钉扎材料体系;发现具有大的电致电阻效应的CMR薄膜材料,并可期望用于电流直接进行磁信息写和读操作的磁存储介质;发现双势垒磁性隧道结中的量子阱态共振隧穿和磁电阻振荡效应,以及纳米器件体系中自旋翻转长度的观测新方法,可用于新型自旋电子学材料及相关器件的人工辅助设计;利用电子自旋共振谱探测和研究了金属氧化物的微观自旋结构和各向异性;在[CoFe/Pt]n磁性金属多层膜中,观测到超高灵敏度的反常霍尔效应;利用纳米环状磁性隧道结作为存储单元,研制出一种新型纳米环磁随机存储器MRAM原理型演示器件.     

自旋阀与多层膜巨磁电阻的特性测量及比较

介绍磁性多层膜中自旋极化输运和巨磁电阻效应,简述自旋阀巨磁电阻与多层膜巨磁电阻在材料组成结构和工作原理方面的区别,利用和改造现有的高校物理实验室中的实验仪器并设计简易的实验电路测量这两种类型的巨磁电阻的磁敏特性,并根据实验测量的结果将这两种传感器在其灵敏度和测量范围上进行比较和研究.     

高自旋极化氧化物材料的颗粒边界磁电阻效应

颗粒边界磁电阻是高自旋极化氧化物颗粒体系中由于颗粒边界的存在而导致显著的磁电阻效应。本文将这种磁电阻效应定义为颗粒边界磁电阻效应。这里所说的颗粒边界,包括各种自然和人工晶界、粉末颗粒表面、复合材料中的颗粒界面等多种情况;所涉及的材料包括高自旋极化氧化物多晶、压缩粉末和各种复合材料等。对颗粒边界磁电阻效应的研究,不仅有助于人们进一步理解高自旋极化氧化物磁输运性质的基本机制,并为寻求具有高磁电阻效应的新型自旋电子学器件提供理论基础。本文综述了高自旋极化氧化物颗粒边界磁电阻研究的主要背景和发展现状,介绍了该领域中主要的实验发现和理论模型,展望了未来的发展。     

高自旋极化氧化物材料的颗粒边界磁电阻效应

颗粒边界磁电阻是高自旋极化氧化物颗粒体系中由于颗粒边界的存在而导致显著的磁电阻效应。本文将这种磁电阻效应定义为颗粒边界磁电阻效应。这里所说的颗粒边界,包括各种自然和人工晶界、粉末颗粒表面、复合材料中的颗粒界面等多种情况;所涉及的材料包括高自旋极化氧化物多晶、压缩粉末和各种复合材料等。对颗粒边界磁电阻效应的研究,不仅有助于人们进一步理解高自旋极化氧化物磁输运性质的基本机制,并为寻求具有高磁电阻效应的新型自旋电子学器件提供理论基础。本文综述了高自旋极化氧化物颗粒边界磁电阻研究的主要背景和发展现状,介绍了该领域中主要的实验发现和理论模型,展望了未来的发展。     

磁电子学讲座 第五讲 自旋极化输运及隧道巨磁电阻效应

简要回顾了利用量子隧道效应测定铁磁金属传导电子自旋极化率的研究历史．综述了自旋极化电子隧穿效应导致的“铁磁金属／非磁绝缘体／铁磁金属”三层平面型隧道结（简称ＦＭ／Ｉ／ＦＭ隧道结）中的巨磁电阻效应以及“铁磁金属／非磁绝缘体”颗粒膜系统中的隧穿类型巨磁电阻效应的研究进展．     

自旋电子学和计算机硬件产业

1988年发现巨磁电阻（GMR）效应，是基于自旋的新电子学的开始。文章介绍观察效应的物理基础，以及这些效应和材料在信息存储上的应用。GMR硬盘（HDD）已经形成了数十亿美元的工业；其后发现的室温隧道磁电阻（TMR）效应已用于制造新关磁随机存储器（MRAM），它正在开创另一个数十亿美元的工业。自旋电子学研究的物理对象是自旋向上和自旋向下的载流子，而传统半导体电子学的对象是电荷为正和电荷为负的载流子，即空穴和电子。电子自旋特性进入半导体电子学，为新的器件创造了机会。为了成功地将电子自旋结合到半导体微电子技术中去，需要解决磁性原子自旋极化状态的控制，以及自旋极化载流子电流的有效注入、传输、控制、操纵和检测。评述了基于电子自旋的新器件原理、新材料的探索以及自旋相干态的光学操纵。     

Giant magnetoresistance in ferromagnet/superconductor superlattices

We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized La0.7Ca0.3MnO3 and high-Tc superconducting YBa2Cu3O7. This large magnetoresistance is reminiscent of the giant magnetoresistance (GMR) in metallic superlattices but with much larger values, and originates at spin imbalance due to the injection of spin-polarized carriers. Furthermore, in contrast to ordinary GMR, the magnetoresistance is intimately related to the superconductivity in the YBa2Cu3O7 layer and vanishes in the normal state. This result, aside from its fundamental importance, may be of interest for the design of novel spintronic devices based on ferromagnet/superconductor structures.     

Spin Polarization and Spin‐Flip Through Phosphorene Superlattice

The spin‐dependent transport properties, including spin polarization and spin‐flip for phosphorene superlattice in the presence of an extrinsic Rashba spin‐orbit interaction (RSOI) based on the transfer matrix method, are studied. The results show that the number of barriers in the superlattice structure plays a dominant role in output spin polarization, which can be used in designing optimized spintronic devices. In addition, by controlling on the Rashba strength, an incident spin‐up electron can be transmitted as a spin‐down electron. Also, it enables to convert the unpolarized incident electronic beam (with zero spin polarization) into an arbitrary output spin polarization, which plays a significant role in qubit circuits.     

TMR与GMR传感器1/f噪声的研究进展

隧道结磁阻(TMR) 传感器及巨磁阻(GMR) 传感器的1/f噪声在低频段噪声功率密度较大, 是影响其低频下分辨率和灵敏度的主要噪声形式. 本文详细介绍了近年来TMR传感器及GMR传感器1/f噪声的特点、来源、理论模型、检测方法及降噪措施等方面的研究进展, 并就隧道结磁阻传感器1/f噪声的物理模型进行了详细解释. 通过纳米模拟软件Virtual NanoLab对不同MgO厚度的Fe/MgO/Fe型磁性隧道结(MTJ) 进行了隧穿概率和TMR变化率的模拟计算, 得到保守估计与乐观估计的TMR变化率, 分别为98.1%与10324.55%, 同时通过MTJ的噪声模型分析了MgO厚度对TMR传感器噪声的影响. 制备了磁屏蔽系数大于10000的磁屏蔽筒并搭建了磁阻传感器1/f噪声的测试平台, 通过测试验证了磁屏蔽系统对环境磁场具有较好的屏蔽效果, 为噪声检测提供了稳定的磁场空间. 最后分析了TMR与GMR中各种因素对传感器噪声的影响, 提出了影响MTJ传感器1/f噪声的因素及一些降噪措施.     

Spin torque transfer structure with new spin switching configurations

Spin torque transfer structures with new spin switching configurations are proposed, fabricated and investigated in this paper. The non-uniform current-induced magnetization switching is implemented based on both GMR and MTJ nano devices. The proposed new spin transfer structure has a hybrid free layer that consists of a layer with conductive channels (magnetic) and non-conductive matrix (non-magnetic) and traditional free layer(s). Two mechanisms, a higher local current density by nano-current-channels and a non-uniform magnetization switching (reversal domain nucleation and growth) by a magnetic nanocomposite structure, contribute in reducing the switching current density. The critical switching current density for the new spin transfer structure is reduced to one third of the typical value for the normal structure. It can be expected to have one order of magnitude or more reduction for the critical current density if the optimization of materials and fabrication processes could be done further. Meanwhile, the thermal stability of this new spin transfer structure is not degraded, which may solve the long-standing scaling problem for magnetic random access memory (MRAM). This spin transfer structure, with the proposed and demonstrated new spin switching configurations, not only provides a solid approach for the practical application of spin transfer devices but also forms a unique platform for researchers to explore the non-uniform current-induced switching process.     

Recent spinterfacial studies targeted to spin manipulation in molecular spintronic devices

Molecular spintronics is an emerging field which evoked wide research attention since the first molecule-based spintronic device has been reported at 2002. Due to the active study over the last few years, it is found that the interfaces in spintronic device, so called spinterface, is of critical importance for many key issues in molecular spintronics, such as enhancing spin injection, lengthening spin transport distance, as well as manipulating spin signals in molecular spintronic devices. Here in this review, recent studies regarding spinterface in molecular devices, especially those impressive efforts devoted on spin manipulation, have been systematically summarized and discussed.     

Magnetic two-dimensional van der Waals materials forspintronic devices

Magnetic two-dimensional (2D) van der Waals (vdWs) materials and their heterostructures attract increasing attention in the spintronics community due to their various degrees of freedom such as spin, charge, and energy valley, which may stimulate potential applications in the field of low-power and high-speed spintronic devices in the future. This review begins with introducing the long-range magnetic order in 2D vdWs materials and the recent progress of tunning their properties by electrostatic doping and stress. Next, the proximity-effect, current-induced magnetization switching, and the related spintronic devices (such as magnetic tunnel junctions and spin valves) based on magnetic 2D vdWs materials are presented. Finally, the development trend of magnetic 2D vdWs materials is discussed. This review provides comprehensive understandings for the development of novel spintronic applications based on magnetic 2D vdWs materials.     

First principles investigation of the spin transport properties in graphene-porphine-graphene nanojunctions

The spin-dependent transport properties of a porphine molecule linking with two zigzag-edged graphene nanoribbon (ZGNR) electrodes have been investigated by using the density of functional theory (DFT) combined with the non-equilibrium Green’s function (NEGF) method. The device shows clearly negative differential resistance (NDR), large tunnelling magnetoresistance (TMR) of 10³ magnitude and nearly 100% perfect spin filter efficiency (SFE) properties, respectively. What’s more, the projected density of states (PDOS), molecular projected self-consistent Hamiltonian (MPSH) eigenvalues and transmission eigenstates were carried out to discuss the transport properties of the ZGNR/Porphine/ZGNR nanojunction. These results suggest that the ZGNR/Porphine/ZGNR device is a promising candidate for multi-functional spintronic devices.     

Time-domain measurement of current-induced spin wave dynamics

The performance of spintronic devices critically depends on three material parameters, namely, the spin polarization in the current (P), the intrinsic Gilbert damping (α), and the coefficient of the nonadiabatic spin transfer torque (β). However, there has been no method to determine these crucial material parameters in a self-contained manner. Here we show that P, α, and β can be simultaneously determined by performing a single series of time-domain measurements of current-induced spin wave dynamics in a ferromagnetic film.     

纳米管中的自旋极化

结构缺陷、掺杂等可以导致纳米管的自旋极化，而自旋极化的纳米管可以利用载流子的自旋状态作为信息载体，实现一维的自旋电子传输。具有不同自旋极化结构的纳米管，根据其电子结构、自旋极化性质和输运性质的不同，可以用于实现不同用途的自旋电子器件。很多有关自旋极化的纳米管的理论和实验工作已经展开，然而其中仍有很多物理问题有待深入研究。