Magnetoresistance of Fe3O4/Au/Fe3O4 and Fe3O4/Au/Fe spin-valve structures

A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe₃O₄ electrodes is presented. Fe₃O₄/Au/Fe₃O₄ spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe₃O₄ layers. By contrast, a negative GMR effect is measured on Fe₃O₄/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe₃O₄/Au interface or an induced spin scattering asymmetry in the Au interfacial layers.     

IrMn基反铁磁自旋阀的巨磁电阻效应

用第一性原理方法研究了在微观尺度具有三重对称磁结构的IrMn合金的反铁磁自旋阀(AFSV)的电子输运.研究表明:基于有序L1₂相IrMn合金的Co/Cu/IrMn自旋阀的巨磁电阻(GMR)效应具有三重对称性,可以利用这一特性区分反铁磁材料的GMR与传统铁磁材料的GMR.基于无序γ相IrMn合金的IrMn(0.84 nm)/Cu(0.42 nm)/IrMn(0.42 nm)/Cu(0.42 nm)(111) AFSV的电流平行平面构型的GMR约为7.7％,大约是电流垂直平面构型的GMR(3.4％)的两倍,明显大于实验中观测到的基于共线磁结构的FeMn基AFSV的GMR. 关键词： 反铁磁自旋阀 巨磁电阻效应 非共线磁结构 电流平行平面结构     

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.     

(CoFe)_(1-x)Ag_x颗粒巨磁电阻薄膜的磁折射效应研究

在线非接触测试巨磁电阻效应对磁电子器件的工业化生产具有重要的意义 .用红外光谱研究了 (CoFe) 1 -xAgx颗粒薄膜的磁折射效应 ,研究表明在红外波段 ,一级近似可以认为巨磁电阻比值与磁折射变化率成正比 ,可以利用磁折射效应作为在线非接触工具测量与自旋散射相关的巨磁电阻效应 .     

Spin valves with CoO as an exchange bias layer

The temperature dependence (50–300 K) of the magnetoresistance and exchange bias field of spin valves with a CoO exchange bias layer have been investigated. At room temperature the GMR effect is enhanced in comparison with spin valves with a FeMn biasing layer. This enhancement increases for decreasing temperature for small Cu thicknesses. No influence of the antiferromagnetism of CoO on the GMR has been observed upon crossing of the Néel temperature.     

Perpendicular giant magnetoresistance in magnetic multilayered nanowires

We present giant magnetoresistance (GMR) measurements performed on electrodeposited Co/Cu multilayered nanowires. The variation of the GMR with the thicknesses of the Cu and Co layers over wide ranges is discussed in the framework of the Valet-Fert model for perpendicular GMR. The interface and bulk spin-dependent scattering parameters as well as the spin diffusion lengths in the nonmagnetic and ferromagnetic layers are extracted from this analysis.     

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。     

Giant magnetoresistance in an electrochemically synthesized regimented array of nickel quantum dots

Giant magnetoresistance (GMR) due toremotespin dependent scattering of electrons has been observed in an electrochemically synthesized structure consisting of a two-dimensional, quasi-periodic array of nickel dots (diameter ∼100 Å) overlayed with a thin copper layer. Current flows exclusively in the copper layer, but the electrons scatter from the magnetic moments on the remote, underlying nickel quantum dots. Since the scattering cross-section depends on the magnetization of the dots, the resistance of the structure can be altered with a magnetic field which then gives rise to the GMR. The magnetoresistance is about 3% of the zero-field resistance up to a magnetic flux density of 2 tesla at room temperature.     

Effect of thermal deformation on giant magnetoresistance of flexible spin valves grown on polyvinylidene fluoride membranes

We fabricated flexible spin valves on polyvinylidene fluoride(PVDF) membranes and investigated the influence of thermal deformation of substrates on the giant magnetoresistance(GMR) behaviors. The large magnetostrictive Fe_(81)Ga_(19)(Fe Ga) alloy and the low magnetostrictive Fe_(19)Ni_(81)(Fe Ni) alloy were selected as the free and pinned ferromagnetic layers.In addition, the exchange bias(EB) of the pinned layer was set along the different thermal deformation axes α_(31) or α_(32) of PVDF. The GMR ratio of the reference spin valves grown on Si intrinsically increases with lowering temperature due to an enhancement of spontaneous magnetization. For flexible spin valves, when decreasing temperature, the anisotropic thermal deformation of PVDF produces a uniaxial anisotropy along the α_(32) direction, which changes the distribution of magnetic domains. As a result, the GMR ratio at low temperature for spin valves with EB α_(32)becomes close to that on Si, but for spin valves with EB α_(31)is far away from that on Si. This thermal effect on GMR behaviors is more significant when using magnetostrictive Fe Ga as the free layer.     

The temperature dependence of the perpendicular giant magnetoresistance in Co/Cu multilayered nanowires

A theory, based on earlier work by Valet and Fert, is first presented to describe the influence of temperature on the perpendicular giant magnetoresistance (GMR) in multilayers. Then we present GMR measurements performed at T=77 K and at room temperature on Co/Cu multilayered nanowires with layer thicknesses ranging from a few nm to 1 μm. We use our model to obtain a good quantitative fit to the experimental results in both the short spin diffusion length limit and out of this limit. We discuss the temperature dependence of the bulk parameters, the scattering spin asymmetry coefficient and spin diffusion length in the Co layers. Received: 25 January 1998 / Accepted: 6 May 1998     

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.     

GMR enhancement in spin valves structures with nano-semiconducting layer

We report on the giant magnetoresistance enhancement in Co/Ru/Co-based spin valve structures with nano-semiconducting layer. The films were grown by ion beam sputtering on glass substrate at room temperature. The soft layer is composed of Fe/Co bilayers, while the hard layer is ensured by the Co/Ru/Co artificial antiferromagnetic subsystem (AAF) as follows: Fe_5nm/Co_0.5nm/Cu_3nm/Co_3nm/Ru_0.5nm/Co_3nm/Cu_2nm/Cr_2nm. This structure shows a giant magnetoresistance (GMR) signal of about 1.7%. To confine the electrons inside the spin valve structure, a 1.5 nm thick ZnSe semiconducting layer has been grown on the top of the AAF. This induces a strong GMR increase, up to 4%, which can be attributed to a dominant potential step at the Co/ZnSe interface.     

GMR effects in graphene-based Ferromagnetic/Normal/Ferromagnetic junctions

In this paper the parallel and antiparallel graphene based Ferromagnet–Normal–Ferromagnet (FNF) structures are investigated theoretically. Effect of parallel and antiparallel alignments strength of ferromagnets and thickness of normal region and temperature on the charge, spin and thermal conductances are studied. A survey on Giant magnetoresistance (GMR) has been done and we have shown that, conductances of parallel and antiparallel structures are different. In this paper, we study and calculate all kinds of the GMR including the charge-GMR, thermal-GMR and also spin-GMR for a FNF systems. Although the charge-GMR is important and useful in fabrication magnetic information storage has been investigated in many works but few papers exist about thermal-GMR and spin-GMR. Also with consideration spin current we observed that, in definite strength of ferromagnetic film and in the presence of charge current, spin current is zero. This latter case can be used as a spin-valve.     

Universal relationship between giant magnetoresistance and anisotropic magnetoresistance in spin valve multilayers

We measure the giant magnetoresistance (GMR) with the current both parallel and perpendicular to the direction of the magnetization in the ferromagnetic (FM) layers and thus probe the anisotropy of the effective mean free paths for the spin-up and spin-down electrons, seen in the anisotropic magnetoresistance. We find that the difference of the GMR in the two configurations, when expressed in terms of the sheet conductance, displays a nearly universal behavior as a function of GMR. On interpreting the results within the Boltzmann transport formalism we demonstrate the importance of bulk scattering for GMR.     

Influence of superparamagnetic regions on the giant magnetoresistance of electrodeposited Co–Cu/Cu multilayers

The room-temperature magnetoresistance (MR) of electrodeposited Co–Cu/Cu multilayers was investigated. Samples were prepared on either a polycrystalline Ti foil or on a silicon wafer covered with a Ta buffer and a Cu-seed layer. The field dependence of the magnetoresistance was analyzed by decomposing the GMR into ferromagnetic (FM) and superparamagnetic (SPM) contributions, whereby the field dependence of the latter could be described by a Langevin function. In order to better understand the influence of the deposition conditions on the GMR in electrodeposited multilayers, the evolution of the relative importance of the two GMR contributions is discussed in terms of the Co dissolution process during the Cu deposition pulse.     

Giant magnetoresistance effect in hybrid ferromagnetic/semiconductor nanosystems

We theoretically investigate the giant magnetoresistance (GMR) effect in general magnetically modulated semiconductor nanosystems, which can be realized experimentally by depositing two parallel ferromagnetic strips on the top of a heterostructure. Here the exact magnetic profiles and arbitrary magnetization direction of ferromagnetic strips are emphasized. It is shown that a considerable GMR effect can be achieved in such nanosystems due to the significant transmission difference for electrons tunneling through parallel and antiparallel magnetization configurations. It is also shown that the magnetoresistance ratio is strongly influenced by the magnetization direction of ferromagnetic strips in nanosystems, thus possibly leading to tunable GMR devices.     

Structural effects in the growth of giant magnetoresistance (GMR) spin valves

An investigation has been made of the thin-film structure and interface morphology of giant magnetoresistance (GMR) spin valves of the cobalt/copper/cobalt (Co/Cu/Co) type that were grown on polycrystalline NiO substrates at three different temperatures (150, 300 and 450 K). Sputter-depth-profile analyses indicate that the quality of the layering in the Co/Cu/Co structure was only slightly better for the 150 K sample than for the 300 K sample. For the 450 K sample, however, the Co/Cu/Co structure showed extensive disruption. The similarity in the depth-profiles for the 150 and 300 K samples indicates the sensitivity of the GMR to subtle structural differences.     

磁电子学讲座 第六讲 巨磁电阻效应在信息存储等领域中的应用

用巨磁电阻材料构成磁电子学新器件，已开始在信息存储领域成功地获得了应用．文章介绍了用于计算机硬磁盘驱动器的巨磁电阻磁头和巨磁电阻随机存储器，描述了它的工作原理、性能特点及发展趋势．指出巨磁电阻材料在传感器方面的应用也令人瞩目，有着广阔的市场前景．     

Dual spin valves with nano-oxide layers

A novel method is proposed for increasing the giant magnetoresistance (GMR) of dual spin valves of the CoFe/Cu/CoFe/Cu/CoFe type by inserting nano-oxide layers (NOLs) into the pinned layers. Using this method, MR ratio of 23.5% was obtained, a value equal to those of specular spin valves with antiferromagnetic oxide, e.g., NiO. This method allows the selection of metallic materials for the antiferromagnetic layer. In addition, we obtained the specularity factor of upper NOLs, 0.8, and that of lower NOLs, 0.7, by calculating Boltzmann equations taking into account the roughness of each interlayer. This model shows that the MR ratio would be 27.5% for dual spin valves with ideal NOLs.     

Intergranular giant magnetoresistance in a spontaneously phase separated perovskite oxide

We present small-angle neutron scattering data proving that, on the insulating side of the metal-insulator transition, the doped perovskite cobaltite La(1-x)Sr(x)CoO(3) phase separates into ferromagnetic metallic clusters embedded in a nonferromagnetic matrix. This induces a hysteretic magnetoresistance, with temperature and field dependence characteristic of intergranular giant magnetoresistance (GMR). We argue that this system is a natural analog to the artificial structures fabricated by depositing nanoscale ferromagnetic particles in a metallic or insulating matrix; i.e., this material displays a GMR effect without the deliberate introduction of chemical interfaces.