NiFe和NiFe／Cr／NiFe薄膜的磁电阻特性与膜厚关系

本文研究了采用离子束溅射技术制备的ＮｉＦｅ薄膜及层状结构ＮｉＦｅ／Ｃｒ／ＮｉＦｅ薄膜的磁电阻特性与膜厚的关系。用四探针法测量薄膜的磁电阻。由实验结果得到磁电阻特性和膜厚及Ｃｒ夹层厚度的关系。分析了ＮｉＦｅ／Ｃｒ／ＮｉＦｅ膜中两层ＮｉＦｅ膜之间存在在反铁磁交换耦合时，磁电阻效为著增强的现象，ＮｉＦｅ／Ｃｒ／ＮｉＦｅ膜各向异性磁电阻系数△ρ／ρａｖ达５．１％。     

NiFe/Ag多层膜在低场下的巨磁电阻行为

用磁控溅射法制备了NiFe/Ag多层膜 ,并从实用角度对NiFe/Ag多层膜的低场巨磁电阻效应作了研究。分析了该膜系列产生低场巨磁电阻效应的机理 ,并进行了实验研究 ,最终获得在低场 (小于 79 6× 2 5 0A/m)常温下有高达 5 0 %巨磁电阻效应的材料     

不连续[NiFe/Ag]_n多层薄膜低场巨磁阻研究

用直流磁控溅射和快速真空磁场退火工艺在玻璃基片上制备了 [NiFe/Ag]n不连续多层膜。从理论上分析了不连续膜低响应、高磁电阻值的机制 ,不连续膜模型介于多层膜模型及颗粒膜模型之间。研究了工艺条件 ,即退火温度、退火时间及空间层Ag厚度对不连续膜巨磁电阻特性的影响 ,并对工艺条件进行了优化 ,在常温下获得巨磁电阻值 13% ,饱和场Hs<80 0A/m ,磁场灵敏度 1 3% / 80Am-1的优质薄膜材料。     

NiFeCr/NiFe/MgO/Ta薄膜制备及热处理研究

采用磁控溅射制备了NiFeCr(4.5nm)/NiFe(10nm)/MgO(4.0nm)/Ta(5.0nm)薄膜,并对薄膜进行真空磁场退火。退火后薄膜磁电阻变化率显著提高,400℃退火后达到3.02%,之后随着退火温度的升高,磁电阻变化率下降。XRD结果表明,薄膜不仅具有很强的NiFe(111)织构,同时还出现了MgO的(111)衍射峰。随退火温度的升高,MgO(111)衍射峰的强度有所降低。     

Cu对NiFe/Cu/NiFe层状薄膜的巨磁阻抗效应影响的研究

用直流磁控溅射方法制备了NiFe/Cu/NiFe层状薄膜 ,研究了Cu膜宽度对NiFe/Cu/NiFe层状薄膜的巨磁阻抗效应的影响 ,结果表明 ,层状薄膜的巨磁阻抗效应随Cu膜宽度发生振荡现象 ;并提出了一个等效电路模型直观地解释了层状薄膜增强巨磁阻抗效应的机理     

非均匀退磁场对NiFe薄膜AMR元件性能的影响

采用磁控溅射制备了NiFe各向异性磁电阻(AMR)薄膜,经过光学曝光及离子刻蚀将NiFe薄膜制成了宽度w=20μm、厚度t=20nm、长度l=2.5mm的AMR元件.测量了NiFe元件的磁电阻效应.考虑沿宽度方向退磁场的非均匀性,计算了磁电阻比率.结果表明,理论和实验符合.     

Ta/NiFe和NiFe/Ta界面反应和"死层"现象的研究

Ta/Ni81Fe19和Ni81Fe19/Ta被广泛应用于磁电阻多层膜结构中。我们发现 ,在Ta/Ni81Fe19/Ta薄膜结构中 ,磁性“死层”的厚度大约为 1 6± 0 2nm。用X射线光电子能谱和图谱拟合技术研究Ta/Ni81Fe19和Ni81Fe19/Ta的界面成分和化学状态发现 ,在两上界面处都发生了反应 :2Ta +Ni=NiTa2 ,因此NiFe的有效厚度减少。利用这个反应也可以合理解释用分子束外延制备的自旋阀多层膜比用磁控溅射制备的自旋阀多层膜的“死层”更薄的现象     

NiFe/Ru薄膜的磁学性能的研究

主要讨论了多层薄膜SiO2/NiFe/Ru的磁学特性,着重研究了保护层Ru对磁性薄膜NiFe的厚度及磁性的影响.采用X射线衍射仪及X射线光电子能谱仪对该薄膜进行了结构测试和深度剖析,并且运用XPSPeak 4.1拟合软件对获得的Ru3d的高分辨XPS谱进行了计算机拟合分析;结果表明,Ru更加适合于做保护层,渴望在自旋电子器件上得到应用.     

热处理时间对NiFe薄膜性能的影响

用磁控溅射法制备了厚度２０－２００ｎｍ的ＮｉＦｅ合金薄膜。研究了热处理时间（及温度）对ＮｉＦｅ薄膜的电阻（电阻率）、各向异性磁电阻比和软磁性能的影响。在一定温度下，经适当时间的热处理可以减小ＮｉＦｅ薄膜的电阻、增大其各和中异性磁电阻比，从而制备出性能较好（各向异性磁电阻比较大、温度稳定性较好）的薄膜磁性材料。     

半导体Si(111)上电沉积NiFe缓冲层薄膜

采用电化学沉积法,在半导体硅片上制备了具有纳米晶粒尺寸的NiFe缓冲层薄膜,并确定了获得Ni80Fe20合金的工艺条件.由SEM形貌观测分析,当薄膜名义厚度＞25 nm时,可形成连续性镀层.I-t暂态曲线及STM结果表明,NiFe薄膜在低过电位下以三维岛状模式生长,在高过电位下以二维层状模式生长,其RMS表面粗糙度最小值仅为0.5 nm.XRD结果表明,薄膜为面心立方Ni基固溶体结构,并具有明显的(111)晶面择优取向.当薄膜组成为Ni80Fe20时,各向异性磁电阻效应(AMR)最大,AMR值为1.8%.     

Perpendicular GMI Effect in Meander NiFe and NiFe/Cu/NiFe Film

We have evaluated the perpendicular giant magnetoimpedance effect (GMI) in both NiFe and NiFe/Cu/NiFe films with meander geometry in the $>$1 MHz high-frequency range. With the magnetic field, the perpendicular GMI effect shows an intense GMI peak value at a certain field. This effect is comparable to the longitudinal GMI effect in both profile and peak value amplitude. The experimental results correspond well with the predictions of a single-domain rotational magnetization model. These findings demonstrate that the deflection of the anisotropy to a perpendicular direction plays an important role in the perpendicular GMI effect.      

NiFe／Cu和NiFe／Mo多层膜的界面结构与巨磁电阻

采用磁控溅射方法制备了ＮｉＦｅ／Ｃｕ和ＮｉＦｅ／Ｍｏ多层膜。测量了厚度不同的Ｃｕ层和Ｍｏ层多层膜的磁性和磁电阻,并用电镜分析了部分ＮｉＦｅ／Ｃｕ多层膜样品。测量到ＮｉＦｅ／Ｃｕ多层膜的室温巨磁电阻随Ｃｉ层厚度振荡的第一、二、三峰。而在ＮｉＦｅ／Ｍｏ多层膜中未发现巨磁电阻效应。讨论了多层膜的界面结构对巨磁电阻效应的影响。     

Preparation and Properties of Amorphous NiFe/Cu/NiFe Thin Films

The amorphous of Permalloy on the copper subtract was studied using composite electroplating method. A portion of hydrogen brings the counteraction on the surface of cathode leading nickel-iron alloys to be anomalous in the process of co-depositing. The results of X-ray diffraction (XRD) show that the Ni-Fe alloys layer is amorphous. The Giant Magneto -Impedance (GMI) effect of Ni-Fe alloys was obtained under the optimal conditions, dependence on the soft magnetic property of Ni-Fe amorphous thin film. As a result, the ratios△ Z/Z of NiFe/Cu/NiFe amorphous thin film are 30% at 40 kHz which is in low frequency. Furthermore, the GMI value of NiFe/Cu/NiFe amorphous thin film with a sandwich structure is higher than that of single-layer ferromagnetic films of the same thickness.     

Template-grown NiFe/Cu/NiFe nanowires for spin transfer devices

We have developed a new reliable method combining template synthesis and nanolithography-based contacting technique to elaborate current perpendicular-to-plane giant magnetoresistance spin valve nanowires, which are very promising for the exploration of electrical spin transfer phenomena. The method allows the electrical connection of one single nanowire in a large assembly of wires embedded in anodic porous alumina supported on Si substrate with diameters and periodicities to be controllable to a large extent. Both magnetic excitations and switching phenomena driven by a spin-polarized current were clearly demonstrated in our electrodeposited NiFe/Cu/ NiFe trilayer nanowires. This novel approach promises to be of strong interest for subsequent fabrication of phase-locked arrays of spin transfer nano-oscillators with increased output power for microwave applications.     

Asymmetry of Magnetization Reversal of Pinned Layer in NiFe/Cu/NiFe/IrMn Spin-Valve Structure

Two types of asymmetry in giant magnetoresistance (GMR) are observed which are not related to a training effect, but indicate different mechanisms of magnetization reversal of the pinned layer in spin-valve (SV) structures for ascending and descending field scans. GMR, exchange bias and coercivity in Si/Ta/NiFe/Cu/NiFe/IrMn/Ta SV-structures were investigated as functions of the thickness of the nonmagnetic spacer. The spacer thickness effects are discussed in correlation with layers microstructure and interfaces morphology variations.     

Nanostructure and chemical characterisation of individual NiFe/Pt multilayer nanowires

NiFe/Pt multilayer nanowires have been successfully fabricated by pulse electrodeposition into the channels of porous anodic aluminum oxide (AAO) templates, and characterized at the nanoscale. Individual nanowires have uniform structure and regular periodicity. The NiFe and Pt layers are polycrystalline, with random orientation fcc lattice structure crystallites and grain sizes 3-10 nm, and the average layer growth rate is 30 nm/s for NiFe and 4 nm/s for Pt. Nanoscale chemical analysis of individual NiFe/Pt nanowires by EDX and EELS shows that they contain alternating NiFe and Pt layers, with a small approximately 1% inclusion of Pt in the NiFe layer due to electrochemical co-deposition.     

Effect of Cu surface segregation on properties of NiFe/FeMn bilayers

The films of NiFe/FeMn with Ta and Ta/Cu buffer layers were prepared by magnetron sputtering. Results show that the exchange bias field of NiFe/FeMn films with Ta/Cu buffer is lower than that of the films with Ta buffer. The crystalline texture, surface roughness and element distribution of these two sets of samples were examined, and there is no apparent difference for the texture and roughness. However, the segregation of Cu atoms on the surface of NiFe in the trilayer of Ta/Cu/NiFe has been observed by using the angle-resolved X-ray photoelectron spectroscopy. The decrease of the exchange bias field for NiFe/FeMn films with Ta/Cu buffer layers is mainly caused by the diffusion of Cu atoms through NiFe layer, which stayed at the interface of NiFe/FeMn film or even intruded into FeMn layer. The present results indicate that Cu segregation through NiFe layer should be suppressed in order to improve the exchange bias field in giant magnetoresistance spin valves with Cu spacer.     

Study of the interfacial magnetism in NiO/NiFe system

The interfacial magnetism of NiO/NiFe bilayers with different NiFe layer thicknesses, produced by DC and RF magnetron sputtering, has been studied by magnetometry and X-ray magnetic circular dichroism (XMCD). In magnetic hysteresis loops, the exchange bias field was found to be inversely proportional to the NiFe layer thickness. The fit using the Meiklejohn and Bean model gives a coupling energy at the NiO/NiFe interface of approximately 0.027 mJ/m². The analysis of the XMCD spectra of Fe and Ni, using the sum rules, shows a reduction of the effective spin magnetic moments in bilayers with NiFe thickness less than 4 nm. This reduction is attributed to hybridization of ferromagnetic and antiferromagnetic atoms d orbitals near the interface and/or formation of antiferromagnetic alloys due to atomic diffusion at the interfaces.     

NiO／NiFe双层膜的制备及其交换耦合作用研究

用直流磁控反射溅射制备ＮｉＯ／ＮｉＦｅ双层膜。在保持ＮｉＦｅ层的厚度２０ｎｍ不变的条件下，发现尽管没有用外加磁场引导单向各向异性，由于底盘旋转等因素的影响，ＮｉＯ（７０ｎｍ）／ＮｉＦｅ（２０ｎｍ）双层结构仍显示较好的单向各向异性，交换耦合场可达３０Ｏｅ以上。通过改变ＮｉＯ层的厚度，溅射气体Ａｒ分压以及溅射气体与反应气体的比例Ａｒ／Ｏ２，研究了反铁磁层厚度以及溅射条件对交换耦合场的影响。