工艺参数对Ni81Fe19薄膜磁性及微结构影响

在不同本底真空和工作气压下制备了不同厚的Ni81Fe19／Ta薄膜,并进行了磁性测量和原子力显微镜分析,结果表明,较厚的薄膜,较高的本底真空和较低的工作气压下制备的薄膜有较大的各向异性磁电阻,其原因是高本底真空和低工作气压导致大晶粒度和低粗糙度,进而降低电子的散射,减小电阻R,增大ΔR/R,而较厚薄膜中,大晶粒度的作用将抵消高粗糙度的负作用,使ΔR/R值增大。     

Dependence of Magnetic Properties and Microstructure of Ni81Fe19 Film on Base Vacuum and Sputtering Pressure

The Ni81Fe19 / Ta films with different NiFe thickness were prepared at different base vacuums and sputtering pressures. The results of magnetic measurement and atomic force microscope (AFM) showed that the films prepared at higher base vacuum and lower sputtering pressure had larger R/R. The reason should be that higher base vacuum and lower sputtering pressure introduce larger grain-size and lower surface roughness, which will weaken the scattering of electrons, reduce the resistance R, and increase R/R.     

真空退火处理CoFe对薄膜结构及磁电阻特性的影响

用粉末冶金方法制备了Co90Fe10,研究了不同退火温度对电子束蒸发方法制备的CoFe薄膜磁电阻特性和微结构的影响。CoFe薄膜在优于5 5×10-4Pa的本底真空度下室温沉积在热氧化Si基片上。随后,样品在3×10-5Pa真空度下分别进行了150℃,280℃,330℃,450℃的60分钟退火处理。靶材的扫描电镜图像显示粉末冶金方法制备的靶材比较疏松。电阻率和磁电阻测量表明450℃退火处理能够明显降低CoFe薄膜电阻率和提高磁电阻变化率。X射线衍射发现沉积在热氧化Si基片上的CoFe膜(111)晶面面间距明显小于靶材相应晶面面间距,退火处理使膜(111)晶面面间距明显减小,趋向靶材面间距。     

缓冲层对NiCo薄膜各向异性磁致电阻的影响

用磁控溅射法制备了以NiFeCr和Ta分别为缓冲层的两种NiCo薄膜样品,在不同温度下对两种样品退火.结果表明:在NiCo厚度相同的情况下,以NiFeCr作为缓冲层的样品的各向异性磁致电阻(AMR)值明显高于Ta作为缓冲层的样品.X射线衍射(XRD)的结果表明,NiFeCr/NiCo薄膜的晶粒平均尺寸大于Ta/NiCo薄膜,且两种样品的磁膜/缓冲层界面存在较大差异,这可能是造成两者AMR差异的原因.此外,对样品进行温度适当的热处理可以明显改善薄膜的物理性质.     

Magnetoresistance of the thin film ferromagnetic nanoconstrictions

The magnetoresistance and I-V characteristics at different temperatures of the thin film ferromagnetic nanoconstrictions of variable width (from 20 to 250 nm) and 10 nm thicknesses, fabricated by electron beam lithography and vacuum thin film deposition are compared. The magnetoresistance and resistance of the thin film ferromagnetic nanoconstrictions are not related to the width of the nanoconstrictions. Instead the resistance of the local nano-region in the middle of the thin film ferromagnetic nanoconstriction has only a minor role compared to that of the two microscale thin film ferromagnetic electrodes, which contribute the majority of the measured resistance. The magnetoresistances of the thin film ferromagnetic nanoconstrictions and a 0.2 cm × 0.8 cm thin ferromagnetic film deposited under the same conditions were also compared; the thin film ferromagnetic nanoconstrictions have higher magnetoresistances than the thin ferromagnetic film, which implies that the measured magnetoresistance of the thin film ferromagnetic nanoconstrictions comes mainly from the local nano-region in their centers. In conclusion, the measured magnetoresistance of the whole sample is similar to the anisotropic magnetoresistance, because the resistance of the two microscale thin film ferromagnetic electrodes is much higher than that of the local nano-region in the middle of the samples. Comparing the experimental results for the thin film ferromagnetic nanoconstrictions and the thin ferromagnetic film reveals that the magnetoresistance of the local nano-region in the middle of the sample is much higher than that of the two microscale thin film ferromagnetic electrodes attached to it.     

磁电阻材料的研究进展

磁电阻效应在基础研究上具有重要意义及广泛的应用前景,寻找既具有低饱和场,又具有高磁电阻效应的磁性材料已成为当前国际上材料研究热点之一.本文介绍了几种磁电阻效应以及磁电阻材料在高密度读出磁头、磁性随机存储器等领域的应用前景.     

Ta种子层厚度及溅射速率对Ta/Ni65Co35双层膜各向异性磁电阻和矫顽力的影响

研究了Ta种子层的厚度、溅射速率对Ta/Ni65Co35双层膜各向异性磁电阻值(△p/p)、矫顽力和织构的影响.研究表明,适当的Ta层厚度和较高的Ta层溅射速率对提高Ta/Ni65Co35双层膜的△p/p是有效的.Ta种子层的使用增大了Ta/Ni65Co35双层膜的矫顽力而其溅射速率对Ta/Ni65Co35双层膜矫顽力的影响很小.     

La0.67Ca0.33MnO3薄膜中的非欧姆行为研究

 用四探针法对不同倾斜衬底La_0.67Ca_0.33MnO₃薄膜进行了不同电流下的电阻温度关系测试,发现了3个结果:①偏电流>1mA时,焦耳热作用使电阻温度曲线的转变点温度下降;②偏电流<1mA时,薄膜的转变点电阻随所加的偏电流的增加而减小,这是对欧姆行为的偏离(即非欧姆行为);③这一偏离随衬底倾斜角度的增加而增加.对经过氧气氛高温退火的La_0.67Ca_0.33MnO₃薄膜进行了测量,发现峰值电阻及峰值电阻的变化明显减小.初步分析的结果是:①大电流的加热效应是峰值温度偏移;②可能是晶界作为隧穿结导致了薄膜中的非欧姆行为.     

Low-field positive and high-field negative magnetoresistances in multiphase Fe-oxide thin films at room temperature

Multiphase Fe-oxide thin films are fabricated on glass substrates by a facing-target sputtering tech- nique. X-ray diffraction and X-ray photoelectron spectroscopy reveal that Fe, Fe3BO4, γ -Fe2BO3B and FeO coexist in the films. High resolution transmission electron microscopy shows the well-defined colum- nar grain structure with the unoxidized Fe as the core and iron-oxide as the shell. The low-field positive and high-field negative magnetoresistances coexist in such a system at room temperature, which can be explained by considering a shell/core model. Nonlinear current-voltage curve and photovoltaic effect further confirm the tunneling-type conduction.     

Cu底层对SmCo薄膜磁性能的影响

通过多靶射频磁控溅射系统在玻璃基片上制备了SmCo/Cu磁性薄膜.采用控制变量法优化了磁性层溅射工艺参数,制备出了矫顽力高达2400 Oe的溅射态SmCo面内磁化膜;通过控制溅射Cu底层时的基片温度,薄膜磁化方向有从面内向垂直方向转变的趋势,并制备出矫顽力达到6215 Oe的垂直面内方向的SmCo/Cu薄膜;利用扫描隧道显微镜(STM)分析SmCo薄膜在不同温度下的表面形貌发现,150℃时薄膜的晶粒尺寸较小有利于改善薄膜磁性能.     

Peculiarity of magnetoresistance of discontinuous ferromagnetic thin films

The magnetoresistive properties of discontinuous ferromagnetic Fe and Co thin films deposited by electron-beam sputtering onto glass substrates at room temperature were investigated. Tunnel magnetoresistance (MR) was observed for all of the as-deposited samples. The maximum MR was observed for Fe thin films with an effective thickness of 17 nm. In the case of the Co thin films, the annealing process led to a change of the type of MR to anisotropic at Co film thicknesses (d_Co) of 15 ≤ d_Co ≤ 25 nm and to positive isotropic at thicknesses of d_Co < 15 nm. By contrast, the MR type of Fe thin films did not change.     

具有立方格点结构的铁磁薄膜的磁化强度和矫顽力

使用变分累积展开法，计算了简单立方、体心立方、面心立方格点上自旋1／2的铁磁薄膜的磁化强度和矫玩力，显示磁化强度和矫顽力不仅依赖于温度和自旋层数，而且还依赖于格点结构．     

Thickness dependence of magnetic properties in DyFeCo films

Films of amorphous DyFeCo were deposited on glass substrates using RF sputtering deposition system. The thickness dependence of the coercivity of DyFeCo films prepared under the same sputtering conditions was investigated.It is found that the composition is nearly thickness independent, while the coercivity is shown to increase with the film thickness increasing at the beginning, then above a certain thickness decrease with the thickness increasing. The thickness dependence of the coercivity is believed to be due to microstructure-induced variations in the short-range order during the film growth.     

Magnetic properties and giant magnetoresistance effect of nanometer Fe-In2O3 granular films

Nanometer ferromagnetic metal-semiconductor matrix Fe-In2O3 granular films are fabricated by the radio frequency sputtering. Magnetic properties and the giant magnetoresistance (GMR) effect of Fex(In2O3)1x granular film samples are studied. The result shows that the magne-toresistance (MR) ratio/0 value of the granular film samples with Fe volume fraction x = 35% is 4.5% at room temperature. The temperature dependence (T = 1.5-300 K) of the MR ratio /0 value of Fe0.35(In2O3)0.65 granular films shows that /0 value below 10 K increases rapidly with the decrease of the temperature, and when T = 2 K,/0 value is 85%. Through the study of the dependence of low field susceptibility on temperature and the hysteresis loops at different temperatures, it has been found that, when the temperature decreases to a critical point TP = 10 K, the change of the structure in Fe0.35(In2O3)0.65 granular films results in the transformation of state from ferromagnetic to spin-glass-like. The remarkable increase of the MR ratio ???/??0 value of Fe0.35(In2O3)0.65 granular films below 10 K seems to arise from the peculiar conducting mechanism of the granular film samples in the spin-glass-like state.     

磁性多层膜的磁滞回线和磁阻曲线的唯像理论研究

基于相干转动的局域能量极小模型和经典的热激活模型研究了包含二次、双二次耦合的磁性多层膜的磁化过程。计算结果表明双二次耦合和磁层的层数对多层膜的磁相图、磁滞回线、磁阻曲线都有重要的影响。在有限温度下，热激活使得磁性多层膜的磁状态间发生跳跃而达到动态平衡。当引入了具有高斯分布的微磁畴元后，计算了系统的磁状态，得到了不同温度下的磁滞回线和磁阻曲线。计算结果较好地解释了形态各异的磁滞回线和磁阻曲线。     

巨磁电阻的若干问题

本文综述了各向异性磁电阻(AMR)．巨磁电阻(GMR)，特大磁电阻效应(CMR)以及隧道磁电阻效应(TMR)的实验结果及理论模型     

Magnetic properties and giant magnetoresistance effect of nanometer Fe−In2O3 granular films

Nanometer ferromagnetic metal-semiconductor matrix Fe−In₂O₃ granular films are fabricated by the radio frequency sputtering. Magnetic properties and the giant magnetoresistance (GMR) effect of Fe_x(In₂O₃)_1−x granular film samples are studied. The result shows that the magnetoresistance (MR) ratio Δρ/ρ ₀ value of the granular film samples with Fe volume fraction x=35% is 4.5% at room temperature. The temperature dependence (T=1.5–300 K) of the MR ratio Δρ/ρ ₀ value of Fe_0.35(In₂O₃)_0.65 granular films shows that Δρ/ρ ₀ value below 10 K increases rapidly with the decrease of the temperature, and when T=2 K, Δρ/ρ ₀ value is 85%. Through the study of the dependence of low field susceptibility on temperature and the hysteresis loops at different temperatures, it has been found that, when the temperature decreases to a critical point T _p=10 K, the change of the structure in Fe_0.35)In₂O₃)_0.65 granular films results in the transformation of state from ferromagnetic to spin-glass-like. The remarkable increase of the MR ratio Δρ/ρ ₀ value of Fe_0.35(In₂O₃)_0.65 granular films below 10 K seems to arise from the peculiar conducting mechanism of the granular film samples in the spin-glass-like state.     

SmCo(Al,Si)/Cr硬磁薄膜的结构与性能

在优化后的磁控溅射和退火条件下 ,制备SmCo(Al,Si) /Cr硬盘磁记录介质及硬磁薄膜 .实验结果表明 ,Sm摩尔分数为 31.6 % ,Cr缓冲层为 6 6nm ,Sm(Co ,Al,Si) 5磁性层为 30nm时 ,制得的Sm(Co ,Al,Si) 5/Cr薄膜的矫顽力Hc 为 187.8kA/m ,剩磁比S =Mr/Ms≈ 0 .94;在 5 0 0℃保温 2 5min退火后 ,矫顽力Hc 达10 42 .5kA/m ,剩磁比S≈ 0 .92 ,从而制成了较理想的硬磁薄膜     

HD处理烧结磁体制备各向异性NdFeB磁粉

研究了通过吸氢破碎(HD)处理由烧结NdFeB磁体制取各向异性磁粉的方法.实验结果表明:HD处理温度是该处理过程中的关键参数,对于最终获得的各向异性磁粉的矫顽力具有显著的影响,同时HD处理温度的变化决定了烧结磁体破碎过程中的断裂方式.当HD处理温度为220℃时,磁体主要以沿晶断裂方式破碎,再经过950℃温度下的热处理,获得的各向异性磁粉的矫顽力达到490kA/m.     

Spintronic materials and devices based on antiferromagnetic metals

In this paper, we review our recent experimental developments on antiferromagnet (AFM) spintronics mainly comprising Mn-based noncollinear AFM metals. IrMn-based tunnel junctions and Hall devices have been investigated to explore the manipulation of AFM moments by magnetic fields, ferromagnetic materials and electric fields. Room-temperature tunneling anisotropic magnetoresistance based on IrMn as well as FeMn has been successfully achieved, and electrical control of the AFM exchange spring is realized by adopting ionic liquid. In addition, promising spin-orbit effects in AFM as well as spin transfer via AFM spin waves reported by different groups have also been reviewed, indicating that the AFM can serve as an efficient spin current source. To explore the crucial role of AFM acting as efficient generators, transmitters, and detectors of spin currents is an emerging topic in the field of magnetism today. AFM metals are now ready to join the rapidly developing fields of basic and applied spintronics, enriching this area of solid-state physics and microelectronics.