金属磁性多层膜的新颖特性──巨磁电阻效应

磁性和非磁性层交替重构成的金属磁性多层膜常具有巨磁电阻效应，其中每层膜约几个纳米厚。出现巨磁电阻效应的基本条件是：在外磁场下相邻磁层磁化强度取向发生对变化。巨磁电阻效应的物理起源是，其自旋与局域磁化强度平行和反平行的电子受到的散射不同，散射的不同既要嗵来自获射中收的特性，又可能源于两种自旋电子的能态密度的差异。由于信息存储技术中磁电阻“读出”磁头有巨大的应用前景，巨磁电阻效应引起了人们的极大兴趣。     

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。     

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。     

(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 .     

磁性金属多层膜中的巨磁电阻效应

在许多磁性金属多层膜系统中都存在巨磁电阻效应，这些系统是由厚度为几个纳米的磁层与非磁层交替重叠构成，出现巨磁电阻效应的必要条件是系统的磁化状态能被外加磁场所改变。该效应的物理是传导电子在界面处或磁层内的所谓自旋相关散射，层间耦合随隔离层厚度变化而振荡的现象，在隔离层为非磁过渡金属和贵金属的系统中普遍存在，自旋阀多层结构在信息存储技术中磁电阻“读出”头方面极具应用前景。     

磁电子学讲座第三讲 磁性金属多层膜中的巨磁电阻效应

在许多磁性金属多层膜系统中都存在巨磁电阻效应，这些系统是由厚度为几个纳米的磁层与非磁层交替重叠而构成．出现巨磁电阻效应的必要条件是系统的磁化状态能被外加磁场所改变．该效应的物理原因是传导电子在界面处或磁层内的所谓自旋相关散射．层间耦合随隔离层厚度变化而振荡的现象，在隔离层为非磁过渡金属和贵金属的系统中普遍存在．自旋阀多层结构在信息存储技术中磁电阻“读出”头方面极具应用前景．     

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。     

磁电阻效应的研究进展

介绍了磁电阻效应的研究状况和进展,总结了铁磁金属的磁电阻效应、磁性多层膜和颗粒膜的巨磁阻效应、磁隧道电阻效应及氧化物铁磁体的超大磁阻效应的理论模型,并简要分析了磁电阻效应的物理机制。     

Fe15.16Ag84.84金属颗粒膜自旋极化相关的霍尔效应研究

采用磁控溅射法分别在玻璃和单晶硅衬底上同时制备了Fe_15.16Ag_{84.84金属颗粒膜样品，并对样品的霍尔效应和霍尔系数RH随外加磁场H的变化关系进行了 实验研究. 观察到霍尔电压UH与外加磁场H的关系曲线呈现出自旋极化相关的反常现象，并 与其磁电阻效应具有对应关系.基于自旋相关的散射理论对此作出了合理的解释. 关键词： 颗粒膜 霍尔效应 c}')" href="#">特征磁场H_c 自旋相关散射     

Co-SiO2颗粒膜的巨磁电阻效应

采用离子束溅射方法在玻璃基片上制备了一系列的Co-SiO2颗粒膜样品,并对样品的巨磁电阻效应进行了研究.在Co35(SiO2)65(体积百分比)颗粒膜样品中,观测到室温下近4%的巨磁电阻效应.研究了不同基片温度对巨磁电阻效应的影响并发现,随着基片温度的升高样品的巨磁电阻效应下降.根据样品的电阻率-温度关系曲线分析,在铁磁金属-非磁绝缘介质颗粒膜中,除了电子自旋相关隧穿效应外,可能还存在其他的导电机制.     

Correlation between the real Co particle size distributions and the magnetic properties of GMR Cu–10Co alloy

The results of transmission electron microscopy (TEM), magnetic and magneto-resistivity investigations of the Cu–10Co (wt%) giant magneto-resistance (GMR) melt-spun ribbons are reported and discussed. To obtain different distributions of ferromagnetic Co particles in a non-magnetic Cu matrix, the alloy was aged at 550 °C for 0.5, 1, 2, 16, and 32 h. Particle size measurements were performed using quantitative TEM metallography methods. Two size classes of Co particles are identified: primary particles (P) precipitated during the melt-spinning process and the secondary particles (S) precipitated during the ageing process. The results of magnetization and coercitivity are correlated with the results of calculations based on the real Co particle distributions determined from TEM micrographs. The behavior of magnetization and coercive force in function of ageing time is explained as related with changes of a mean particle size. It is shown that the GMR effect is not influenced by Co particles distribution for the S particles with the mean size less than 10 nm, whereas for Co distributions with larger mean diameters, the GMR effect is strongly reduced.     

Micromagnetic simulations on detection of magnetic labelled biomolecules using MR sensors

In this work, we present a study of the interaction between the magnetic particles used in biological applications and the giant magnetoresistive effect (GMR) sensor. The fractional change in resistance, and hence the sensitivity, will be maximized by matching, as far as possible, the size of the sensor to the size of the beads and by carefully positioning the beads over the sensor. We found, by micromagnetic simulations, that the amount of the surface coverage with magnetic particles may affect the magnetization curve of the sensor and will change the field dependence of the GMR response.     

Temperature dependence of GMR and effect of annealing on electrodeposited Co-Ag granular films

The magnetoresistance of Co-Ag granular films composed of superparamagnetic and ferromagnetic particles was studied at different temperatures. The increase in the GMR values while decreasing temperature down to 20 K was quantified. The non-saturating behaviour of the MR(H) curves was retained even at the lowest measurement temperature, which was mainly attributed to the dipolar interaction among the superparamagnetic particles. The influence of the annealing conditions on the magnetoresistance was also studied. In all conditions, a decrease in the GMR values was measured being attributed to an increase in the particle size.     

Well-defined Co clusters embedded in an Ag matrix: A model system for the giant magnetoresistance in granular films

Well-defined granular Co/Ag films have been prepared by the co-deposition of in-beam prepared Co clusters and Ag atoms. In this way we were able to study the giant magnetoresistance (GMR) as a function of mean Co cluster size for a fixed Co cluster volume fraction v_cl as well as a function of v_cl for a fixed . Mean Co cluster size has been varied between and 6.9 nm, Co cluster volume fraction between 5 and 43%. The GMR was measured in-situ at T=4.2 K in magnetic fields 1.2 T. The analysis of the GMR data obtained from these studies clearly shows that spin-dependent scattering at the Co-cluster/Ag-matrix interface is the only relevant scattering mechanism causing the GMR in our well-defined samples. Received: 21 April 1998 / Received in final form: 17 May 1998 / Accepted: 18 May 1998     

磁性多层薄膜系统中的巨磁电阻效应

考虑到量子尺寸效应以及来自杂质、粗糙表面、粗糙界面三方面的散射,运用量子统计格林函数方法和久保理论,计算了磁性多层薄膜系统中的巨磁电阻,讨论了巨磁电阻随非磁层厚度作周期性振荡,以及在(Fe/Cr)_N/Fe系统中巨磁电阻随多层基元数目N增加而增大等现象.理论计算与实验结果符合.此外,还讨论了有关各种散射引起的散射率能否相加的问题. 关键词：     

Magnetic properties and giant magnetoresistance in electrodeposited Co–Ag granular films

Small cobalt particles embedded in a silver matrix have been prepared using the electrodeposition technique. The size of the clusters is controlled by the deposition potential and the Co growth time. Structural, magnetic and magneto-transport properties of Co–Ag samples have been investigated as a function of the Co concentration between 2 and 40 at% cobalt. Superparamagnetic behavior is evidenced for the low contents of cobalt while long-range magnetic order appears at higher Co concentrations. The particles size has been determined from magnetic properties and from the X-ray diffraction technique, and varies between 3.5 and 9 nm. Magnetoresistance passes through a maximum as a function of the cobalt concentration. A maximum of ∼4% GMR is obtained at room temperature while GMR reaches a value of 14% at 10 K.     

不同过渡层上Co/Cu/Co三明治结构的巨磁电阻效应研究

通过对不同过渡层上Co(5.5nm)/Cu(3.5nm)/Co(5.5nm)三明治结构的研究,发现过渡层的磁性及过渡层诱导的三明治晶格结构对材料的巨磁电阻效应有重要影响.反铁磁Cr过渡层由于和相邻铁磁Co层之间存在着反铁磁耦合,可以获得6％以上的巨磁电阻值,但它同时使材料的矫顽力较大,因此磁灵敏度不高.Ni和Ti过渡层上Co/Cu/Co三明治结构,由于形成了强的（111）织构,其巨磁电阻值也达到5％以上.磁性材料Ni过度层还使三明治结构材料的矫顽力大为下降,从而显著提高了材料的磁灵敏度. 关键词：     

Micromagnetic Simulation of Transfer Curve in Giant-Magnetoresistive Head

The transfer curve of the giant-magnetoresistive （GMR） magnetic head represents its most important property in applications, and it is calculated by the micromagnetic modeling of the free layer and the pinned layer in the heart of the GMR head. Affections of the bias hard magnetic layer and the anti-ferromagnetic pinning layer are modeled by effective magnetic fields. The simulated transfer curve agrees with experiment quite well, therefore the values of these effective magnetic fields can be determined by the model. A synthetic antiferromagnetic spin valve structure GMR head is also analyzed for comparison.     

Quantum analytical theory for giant magnetoresistance in magnetic multilayered film systems

Taking into account the quantum size effects and considering three types of scattering from bulk impurities, rough surfaces, and rough interfaces, we use the quantum-statistical Green's function approach and Kubo theory to calculate the giant magnetoresistance (GMR) in magnetic multilayered structures. Our calculation can reproduce the main features of GMR experiments, including the oscillations of GMR with nonmagnetic thickness, and the GMR increases with increasing number of bilayers N of the (Fe/Cr)_N/Fe system and others. As well, the question whether or not the scattering rates due to the impurities, surfaces, and interfaces add up is also addressed to.     

Correlation between magnetotransport properties and the microstructure of the Co20Cu80 granular alloy

We report on the structural, transport and magnetic properties of Co₂₀Cu₈₀ metallic granular films. The granular films are prepared by ion-beam sputtering at room temperature on glass substrates. The structural properties have been investigated using X-ray diffraction and transmission electron microscopy. Structural characterisation confirmed that the samples consist of fine magnetic particles embedded in the non-magnetic Cu matrix. Giant magnetoresistance (GMR) of 3% is observed at room temperature after annealing at 250°C for 30 min. Detailed structural analysis is performed to understand the origin of the small GMR signal. It is confirmed that this result is directly correlated to the small size, density, and non-uniform distribution of Co particles.