MAGNETORESISTANCE EFFECT OBSERVED IN Fe／Mo MULTILAYERS PREPARED BY ELECTRON BEAM EVAPORATION

The Fe/Mo multilayers were prepared by electron beam evaporation, the micro structure and magnetic properties of the multilayers were studied by X-ray diffraction, vibrating-sample magnetometer (VSM) et al. The experimental results revealed that the Fe/Mo multilayers in our experimental conditions behaved magnetoresistance effect with a sharp peak on magnetoresistance (MR) ratio curve, and magnetoresistance is easily saturated at low applied magnetic fields. For [Fe(1.5nm)/Mo(1.0nm)]4,2 multilayers, MR ratio could arrive to 0.1%. The antiferromagnetic interlayer coupling could be observed in some films at room temperature. The strength of the antiferromagnetic interlayer coupling J in the films is low because of the low saturation field Hs. The relationship between magnetic properties and micro structure was also discussed in this paper.     

Effect of annealing on the structural properties of AlN thin films containing Co particles

This paper describes a new approach for preparing AlN thin films containing various Co contents by using a two-facing targets type sputtering system. The as-deposited films exhibited a variable nature expected from the AlN-rich phase, as well as an amorphous-like phase, depending on the Co content in the films. The films were annealed isothermally at different temperatures and their microstructure, magnetic properties and resistivity were examined. The saturation magnetization of the as-deposited films was quite small and almost constant, irrespective of the Co content in the films, because Co was not in the crystalline state. At elevated annealing temperatures, the as-deposited AlN-Co amorphous films crystallized into two phases of AlN and Co. The saturation magnetization and resistivity of the films increased with increasing annealing time and temperature. The coercivity of the films was independent of the annealing time, but it increased with increasing annealing temperature due to the increase in grain size. A saturation magnetization, coercivity and resistivity of 360 emu/cm³, ～25 Oe and 2200 μΩ-cm, respectively, were obtained. Further improvement in the soft magnetic properties might lead to this material being applied as a high density magnetic recording head material.     

[Co／Ti],[Co／Cu（Ni）]多层膜的结构与磁性

用双对向靶溅射方法制备了具有非晶磁性的「Ｃｏ／Ｔｉ」３０，「Ｃｏ／Ｃｕ（Ｎｉ）３０」两组多层膜，分别用Ｘ射线衍射，透射电镜和振动样品磁强计做了结构和磁性测量，在以非晶Ｃｏ和Ｃｉｕ－Ｎｉ合金构成的「Ｃｏ／Ｃｕ（Ｎｉ）」多层膜中，发现饱和磁化强度Ｍｓ随非磁性层厚度ｄｓ的增国发生振荡变化；在以非晶Ｃｏ和Ｔｉ构成的「Ｃｏ／Ｔｉ」多层膜中，ＭＳ和则随ｄｓ的增加而减小。     

CoCu合金颗粒膜的室温磁电阻效应

利用射频磁控溅射方法制备ＣｏＣｕ合金不同成分的亚稳态薄膜。研究了ＣｏＣｕ合金颗粒膜的磁电阻随真空退火温度、外磁场以及组元成分而变化的规律。经真空退火后，ＣｏＣｕ颗粒膜中析出的Ｃｏ颗粒呈面心立方结构。这种在非磁性Ｃｕ的基体上和具有磁性Ｃｏ偏聚态的纳米级颗粒膜具有巨磁阻（ＧＭＲ）效应。ＣｏＣｕ颗粒膜的ＧＭＲ效应及磁性能均取决于Ｃｏ颗粒的尺寸及数量。     

Spin-valve magnetoresistance in Co/Si/（Co/Cu/Co） multilayers

A series of Co/Si/（Co/Cu/Co） multilayers and Co/Si/Co sandwiches were prepared by high vacuum electron-beam evaporation. It was found that a Si spacer （≥0.9 nm） could greatly decrease the interlayer coupling in Co/Si/Co sandwiches and there was no magnetoresistance（MR） or spin-valve MR in them due to the high resistivity of Si spacer. While in Co/Si/（Co/Cu/Co） multilayers, we observed a spin-valve MR of about 0.5% through a nominal 2.7 nm Si spacer at room temperature. The spin-valve MR in Co/Si/（Co/Cu/Co） multilayers was attributed to the enhanced spin polarization of conduction electrons caused by the top Co/Cu/Co sandwich with GMR mechanism and high spin-dependent scattering at Co/Cu interface.     

Behavior of magnetic and magnetoresistive properties of nanocrystalline Co/Cu/Co films during step-by-step annealing

Three-layered Co/Cu/Co films with d _Cu = 1.0 and 2.1 nm (corresponding to the first and second antiferromagnetic maxima, respectively) and single-layer Co films produced during the same manufacturing cycle of magnetron sputtering in an argon atmosphere have been studied. The behavior of the coercive force and magnetoresistance ratio during step-by-step annealing in a temperature range of 250–400°C has been investigated. The correlation factor between the magnetoresistance ratio and saturation field (or the energy of indirect exchange coupling between Co layers) upon step-by-step annealing is 0.97 and 0.95 for the first and second antiferromagnetic maxima, respectively. In a temperature range of 20–300°C, the correlation factor between the coercive force and saturation field is 0.98–0.99. At T _an > 350°C corresponding to intense grain growth, the violation of the correlation between H _c and H _s takes place. Limits of the time and temperature stability of the Δρ/ρ ratio and H _c during the step-by-step annealing of the films have been determined. The behavior of Δρ/ρ, H _c, and magnetic anisotropy of the three-layered films is shown to be due to structural changes (grain size, amplitude of roughness). The behavior of the magnetic anisotropy constants K _u ¹ and K _u ² depends on the annealing temperature and thickness of the nonmagnetic spacer.     

Giant Magnetoresistance of Metallic Exchange-Coupled Multilayers and Spin Valves

The microstructure and the magnetic and magnetotransport properties have been investigated depending on the types of the magnetic and nonmagnetic materials, composition, nanostructure, and regimes of thermomagnetic treatments for two types of metallic nanostructures, namely, magnetic multilayers and spin valves, which exhibit the effect of a giant magnetoresistance (GMR). Magnetosensitive materials that are promising for the applications in microelectronics have been synthesized: CoFe/Cu multilayers with record values of the GMR effect (81%); NiFeCo/Cu multilayers with a sensitivity of 0.5%/Oe; and microobjects prepared on the basis of spin valves, which possess the anhysteretic field dependence of the magnetoresistance and a GMR effect equal to 9%. Special attention is given to the methods of decreasing hysteresis. A comparison of the obtained results with the results for similar types of materials published earlier has been carried out.     

热处理对FeCuNbSiB单层膜磁性能的影响

本文研究了热处理对FeCuNbSiB薄膜结构及磁性能的影响。XRD分析表明制备态的FeCuNbSiB为非晶态,并且在300℃热处理仍然保持非晶态。300℃热处理后,薄膜释放应力,软磁性能有所提高。热处理温度进一步升高,薄膜由非晶态转化为纳米晶,矫顽力及饱和磁化场明显增加,磁矩向垂直膜面方向转动,软磁性能下降。     

Magnetic anisotropy of Co/Cu/Co nanocrystalline films upon magnetic annealing

The magnetic anisotropy of Co/Cu/Co films with the thickness of the copper spacer corresponding to the antiferromagnetic and ferromagnetic indirect exchange coupling between Co layers has been studied. The films deposited on naturally oxidized (111) Si single crystals were produced by magnetron sputtering. The films were annealed at 240°C. Such an annealing virtually neither changes the grain size nor leads to the mixing of layers; i.e., no disturbance of the coupling type between the cobalt layers takes place. Changes in the surface and induced magnetic anisotropy and in the effective energy of indirect exchange coupling have been studied upon annealing in the presence and absence of a magnetic field. It has been found that the shape of surface inhomogeneities in the films changes upon annealing in the magnetic field applied along the film plane, which substantially affects, the surface anisotropy. In the films characterized by antiferromagnetic coupling, the easy axis of magnetization is induced only in the magnetic fields exceeding the saturation field. The induced-anisotropy constant estimated theoretically agrees well with those determined experimentally.     

大块非晶Nd_(60)Fe_(20)Co_(10)Al_(10)合金在晶化过程中磁粘滞行为的研究

通过铜模吸铸法制备出了Nd_(60)Fe_(20)Co_(10)Al_(10)大块非晶合金,研究了该合金在晶化过程中的结构与磁性能,并利用等待时间法研究了其在晶化过程中的磁粘滞行为,结果表明:在453~783 K温度退火时,合金的磁性能变化不大。当退火温度高于783 K时,合金的剩余磁化强度(M_r)、饱和磁化强度(M_s)和矫顽力(_iH_c)的值均急剧降低,在803K退火后,合金完全晶化,铁磁性消失。当合金在703和753 K退火后,合金的激活体积v_a和激活直径Da的数值变化不大,而合金的扰动场H_f则呈现先上升后下降的现象,并且在703 K时达到最大值,这是因为703 K样品中存在的亚稳相造成了扰动场的增加。此外,还讨论了这些微观磁性参数与合金宏观磁性能的关联性。     

Effect of high magnetic field on the crystallization of Nd2Fe14B/α-Fe nanocomposite magnets

Nd8.1Dy0.9Fe76.95Co8.55B5.5 nanocomposite magnets annealed with and without a 10 T magnetic field were investigated in this article. The ribbons with coexisting amorphous and crystalline phases were selected to do this study. The results of Mossbauer spectroscopy revealed that the content of α-Fe increased when annealed in high strength magnetic field.The size of the grains also increased considerably after the application of magnetic annealing. All these led to the decrease of the magnetic properties, especially the coercivity of the ribbons.     

Magnetic properties of nanocrystalline FeMCuNbSiB alloys (M: Co,Ni)

The magnetic properties and microstructure of nanocrystalline FeMCuNbSiB alloys (M: Co, Ni) annealed under a transverse field have been studied. Large induced magnetic anisotropy and good properties in the high frequency range were obtained in Co-rich nanocrystalline FeCo(Cu)NbSiB alloys.     

Temperature Dependence of Permeability of Co66Fe4Mo2Si16B12 Alloy

At different annealing temperatures, the saturation magnetostrictions and the correlation between the permeability μi and the temperature T (μi-T curves) of the Co66Fe4Mo2Si16B12 alloy were investigated using a small-angle magnetization tester and core tester. The experimental results showed that the μi-T curves had different shapes at different ranges of annealing temperature;the permeability μi of the alloy improved with the increase of the annealing temperatures below 460℃; when the alloy was annealed above 480℃, the poor magnetic properties were considered to be caused by larger saturation magnetostriction.     

Structure and magnetic properties of mechanically alloyed Tb0.2Pr0.8(Fe0.4Co0.6)1.93 and magnetostriction of its epoxy composite

The C15 Laves phase with composition Tb0.2Pr0.8(Fe0.4Co0.6)1.93 was synthesized by mechanical alloying (MA) and subsequent annealing process. The structure and magnetic properties of Tb0.2Pr0.8(Fe0.4Co0.6)1.93 were investigated by means of X-ray diffraction (XRD), a vibrating sample magnetometer, and a standard strain technique. The effect of annealing on the structure and magnetic properties was studied. The analysis of XRD shows that the high Pr-content Tb0.2Pr0.8(Fe0.4Co0.6)1.93 alloy with the single phase of MgCu2-type structure can be success-fully synthesized by MA method. The sample annealed at 450℃ is fotmd to have a coercivity of 196 kA/m at room temperature. An ep-oxy/Tb0.2Pr0.8(Fe0.4Co0.6)1.93 composite was produced by a cold isostatic pressing technique. A large magnetostriction of 400 ppm, at an ap-plied magnetic field of 800 kA/m, was found for the composite. The epoxy-bonded Tb0.2Pr0.8(Fe0.4Co0.6)1.93 composite combines a high mag-netostriction with a significant coereivity, which is a promising magnetostrictive material.     

Fe/Ru界面对多层膜磁性的影响

采用高分辨透射电镜结合振动样品磁强计研究了Fe/Ru多层膜,对不同层厚的Fe/Ru多层膜的界面结构及其对磁性能的影响进行了分析。Fe层很薄时薄膜不连续,岛状分布的Fe颗粒使多层膜显示超顺磁特性。Fe/Ru界面的高分辨电镜观察发现,界面存在粗糙度的不对称性,它是多层膜中产生正磁阻的重要原因。Fe/Ru多层膜的负磁阻在退火后得到较大的提高,表明Fe/Ru多层膜的负磁阻主要来源于界面的粗糙度。     

Co/Pt multilayer-based pseudo spin valves with perpendicular magnetic anisotropy

Pseudo spin valves(SVs) exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers. The selection criteria are square magnetic hysteresis loops, weaker current shunting effect, and proper coercivity. The optimal reference layer and free layer are Pt(5.0 nm)/[Co(0.4 nm)/Pt(0.6 nm)]3/Co(0.4 nm)/Cu(3.0 nm)and Cu(3.0 nm)/[Co(0.4 nm)/Pt(1.5 nm)]4, respectively.The resulting pseudo SV exhibits two well-separated hysteresis loops when the field is applied perpendicular to the film plane. The minor hysteresis loop corresponding to the free layer shifts toward negative direction of the magnetic field axis, indicating ferromagnetic interlayer exchange coupling between the two magnetic layers. The coupling also enhances the coercivity(HC) of both layers. The perpendicular giant magnetoresistance(GMR) of 2.7 % is achieved with current in plane measurement. The GMR first increases when Pt seed layer is thickened, reaches a maximum of 3.0 % at 4 nm and then decreases with the further increase of thickness. But thicker Cu spacer layer always lowers the GMR of the SV.     

Soft-Magnetic High-Entropy AlCoFeMnNi Alloys with Dual-Phase Microstructures Induced by Annealing

The simultaneous enhancement of magnetic and mechanical properties is desirable but challenging for soft-magnetic materials.A fabrication strategy to meet this requirement is therefore in high demand.Herein,bulk equiatomic dual-phase AlCoFeMnNi high-entropy alloys were fabricated via a magnetic levitation induction melting and casting process followed by annealing at 700-1000℃,and their microstructures as well as mechanical and magnetic properties were investigated.The as-cast alloy possessed a single metastable B2-ordered solid solution that decomposed upon annealing into a dual-phase structure comprising an Al-and Ni-rich body-centered cubic(BCC) matrix and Fe-and Mn-rich face-centered cubic(FCC)precipitates both in the grain interior and along the grain boundaries.The magnetic and mechanical properties were closely related to the relative volume fraction of FCC in the alloy.The FCC volume fraction could be increased by increasing the annealing temperature,thereby offering tunable properties.The optimal annealing temperature for balanced magnetic and mechanical properties was found to be 800℃.The alloy annealed at this temperature had an average BCC grain size of 12±3μm and FCC volume fraction of 41±4%.Correspondingly,the s aturation magnetization and coercivity reached 82.57 Am~2/kg and 433 A/m,respectively.The compressive yield strength and fracture strength were 1022 and 2539 MPa,respectively,and the plasticity was 33%.Owing to its adjustable microstructure and properties,the AlCoFeMnNi alloy has potential for use as a multi-functional soft-magnetic material.     

Spin valves based on amorphous ferrimagnetic Gd–Co films

Multilayer Gd–Co/Co/Cu/Co structures were prepared by magnetron sputtering. An analysis of the magnetic and resistive properties allows us to classify these structures among spin valves which demonstrate the giant magnetoresistance effect. The mechanism of the sign reversal of giant magnetoresistance with changing thickness of the Co layer, which is exchange coupled with the ferrimagnetic Gd–Co layer, has been interpreted.     

Thermal stability and magnetic saturation of annealed nickel-tungsten and tungsten milled powders

Crystal structures, microstructures and magnetic saturation of annealed pure W powder along with W-40 wt.% Ni powder mixtures processed by high-energy ball milling were investigated using XRD, DTA, SEM and saturation magnetization techniques. Thermally induced transformations occurred at low temperature annealing. Supersaturated metastable Ni(W) solid solution formed during mechanical milling decomposed during annealing treatment into FCC Ni-rich, FCC W-rich phases and an eta-type phase which was constituted of BCC lattice of W enveloped by two FCC lattices of Ni and W. The structures of the major annealing products were close to Ni₁₀W and W₃Ni₂. The magnetic saturation of the milled W powder and W-Ni mixtures decreased with the increase in annealing temperature. Milling time was more influential on the magnetic properties of the annealed pure W powders.