Magnetic Properties of Fe/Cr Layers Studied by Monte Carlo Simulations

The magnetic properties of antiferromagnetic Fe/Cr layers have been studied using Monte Carlo simulations within the Ising model framework. The considered Hamiltonian includes the exchange interactions between Cr–Cr, Fe–Fe and Cr–Fe and the external magnetic field. The thermal magnetizations of Fe/Cr layers are computed for a fixed size. The critical temperature is deduced. In addition, the magnetizations versus the external magnetic field are also established.     

Fe为过渡层的Co/Cu/Co三明治巨磁电阻效应的研究

用超高真空电子束蒸发方法成功制备了以不同厚度Fe为过渡层的Co/Cu/Co三明治巨磁电阻样品,与以Cr为过渡层的Co/Cu/Co三明治巨磁电阻样品比较,样品的矫顽力大大减小,因而样品的磁灵敏度有了较大地提高。当Fe过渡层的厚度为7nm时样品的磁电阻值最大。另外,温度更强烈地影响以Fe为过渡层样品的磁电阻值,在77K下样品的磁电阻曲线表现出明显的不对称性,它来源于低温下fcc Fe过渡层的反铁磁性转变。     

Correlation of Magnetic Properties of Co/Cr Bilayer Thin Films with Grain Boundary Diffusion

The microstructure and magnetic properties of Co/Cr bilayer films were examined before and after postdeposition annealing by using transmission electron microscopy (TEM), X-ray diffraction (XRD) technique and vibrating sample magnetometer (VSM). A model of grain boundary (GB) Cr-rich phase growth involving GB diffusion derived from the Cr underlayer was proposed to elucidate the kinetics of the paramagnetic Crrich phase growth along Co GBs within the Co layer. The correlation of the GB Cr-rich phase formati...     

Cu对C041Ni33Al26合金马氏体相变和磁性转变的影响

采用金相显微技术、DSC、VSM方法,研究了Cu含量x(x=3,5,8)对Co41Ni33Al26合金马氏体相变和Curie点的影响.结果发现在x≤5%范围内,Co41Ni33-xAl26Cux合金马氏体相变温度与x的关系成直线变化,x每增加1%,马氏体相变温度降低约44K;其Curie点随x增加而缓慢下降,x每增加1%,Curie点约降低3.6K.与L10马氏体结构的Co41Ni33-xAl26Cux(x=0,3,5)合金相比,具有B2结构的Co41Ni25Al26Cu8合金易磁化,并且饱和磁化强度低.     

Surface Morphology, Structural and Magnetic Properties of Electrodeposited NiFeCu/Cu Films

The magnetic and structural properties of the NiFeCu/Cu films electrodeposited on polycrystalline titanium (Ti) substrates and their characterizations were studied. The structural analysis by X-ray diffraction (XRD) has revealed that all films have face-centred cubic (FCC) structure. On the other hand, the XRD analysis showed that the degree of (111) texture is dependent on the Cu content within the film. The composition analysis was carried out by energy-dispersive X-ray spectroscopy (EDX). The result of EDX indicated that the Cu content within the film increases with increasing of non-magnetic Cu layer thickness. The hysteresis loops of the films measured by vibrating sample magnetometer (VSM) showed that all films have a small coercivity typical for soft magnetic materials. The surface morphological structure of the films was investigated by atomic force microscopy (AFM). AFM images indicated that all films have main grains (globular islands) and smaller secondary grains on the main grains with different sizes. The differences observed in the magnetic properties of the films were attributed to the Cu content within the films.     

缓冲层Ta对退火Co/Cu/Co薄膜微观结构和界面互扩散的影响

用直流磁控溅射法在Si/SiO₂基底上制备了Co/Cu/Co薄膜和加入缓冲层的Ta/Co/Cu/Co薄膜,用扫描电子显微镜、原子力显微镜、X射线衍射和俄歇电子能谱研究了薄膜的微观结构、表面形貌、织构和界面互扩散现象。结果表明:退火后薄膜中均存在{111}和{002}衍射峰,加入缓冲层Ta后,Co/Cu/Co薄膜的衍射峰强度明显增强,并存在较强的{111}纤维织构,薄膜表面孔洞及粗糙度大幅减小。退火后薄膜界面处产生互扩散现象,层状结构被破坏。缓冲层Ta提高了薄膜与基底材料间的润湿性,可有效缓解界面互扩散现象。     

Effect of Annealing Temperature on Structural and Magnetic Properties of Zn0.94Co0.05Cu0.01O

The doped ZnO system Zn_0.94Co_0.05Cu_0.01O (ZCCO) was prepared as a nano-polycrystalline by a simple sol–gel process, then air annealed at different temperatures. Applying X-ray diffraction (XRD) and the Rietveld method, structural analysis showed that Co and Cu replace Zn substitutionally yielding ZCCO single phase. The refined u-fractional coordinate of Zn increases monotonically by an annealing temperature from 0.3546 at 500 °C reaching 0.3722 at 800 °C, very near from the ideal value 0.375. The Zn tetrahedrons become more symmetric and the distortion is gradually relieved by annealing up to 800 °C. Annealing at 900 °C introduces tetrahedron distortion in an opposite way. The zero field cooled (ZFC) and field cooled (FC) magnetization versus the temperature at different applied fields and the magnetization versus the applied field at different temperatures were carried out. The system exhibits a ferromagnetic behavior at room temperature. As the annealing temperature increases from 550 to 900 °C, the saturation magnetization at 300 K increases from 0.0507 to 0.1088 emu/g.     

Magnetization behaviour in ultrathin Co/Cu/Ni/Cu(001) trilayers

The magnetization of ultrathin multilayer systems depends in a very sensitive way on their composition. We consider the temperature dependence of magnetization and its orientation in three types of trilayers: 2ML Co/2ML Cu/4ML Ni/Cu(001), 1ML Co/2ML Cu/4ML Ni/Cu(001) and 1ML Co/2ML Cu/3ML Ni/Cu(001). The composition of each system leads to different interdependence of ordering temperatures characterizing the ferromagnetic films. It is shown that in all cases the sublayer magnetizations change gradually their directions as a function of temperature. The use of Néel sublattices concept in Valenta approach allows us to present all dependences in a layer resolved mode which leads to the conclusion that the spin reorientation process runs through non collinear magnetic superstructures.     

New Heusler Compounds Cr2YSb (Y=Fe, Co and Ni): Magnetic and Electronic Properties

The electronic and magnetic properties of the Cr₂YSb (Y=Co, Fe, and Ni) Heusler alloys with both CuHg₂Ti-type and AlCu₂Mn-type structures have been investigated using first-principles calculations based on density functional theory (DFT). Two nearly half-metallic ferrimagnets (HMFs), Cr₂CoSb, and Cr₂FeSb in CuHg₂Ti-type structure, are predicted. The energy gap lies in the minority spin band for both alloys. The calculated total spin magnetic moments are 2μ _B and 1μ _B per unit cell for Cr₂CoSb and Cr₂FeSb alloys, respectively, which are in good agreement with the Slater–Pauling relation. For these alloys, the magnetic moments of Y and Cr(B) are antiparallel to that of Cr(A) and all of these moments increase with increasing lattice constant. It was also found that the half-metallic properties of Cr₂CoSb and Cr₂FeSb are unaffected to the lattice distortion and the half-metallicity can be obtained within the wide range of 5.52–6.07 Å and 5.96–6.16 Å for Cr₂CoSb and Cr₂FeSb alloys, respectively.     

钴、镍纳米线及其异质结的制备与磁性研究

采用脉冲电沉积技术在氧化铝模板中制备了单晶钴、镍纳米线阵列和镍/钴纳米线异质结阵列.分别用场发射扫描电镜、透射电镜、X射线衍射仪、物理性能测试系统对纳米线阵列的微观形貌、结构和性能进行了表征与研究.结果表明,所制备的磁性纳米线有很大的长径比,易磁化方向均为纳米线长轴方向.纳米线异质结阵列在易磁化方向具有较大的矫顽力和矩形比,可用作高密度垂直磁记录材料.     

Structural and magnetic characterization of electrodeposited Ni/Cu multilayers

Ni/Cu multilayers were electrodeposited from a single solution electrolyte by galvanostatic method. Interface roughness, magnetization and magneto-transport studies of Ni/Cu multilayers on Si(1 1 1)/Ti/Cu substrate were carried out for samples deposited from three different electrolytes, viz. pure sulphate, sulphate–citrate and sulphate-polyethylene glycol-8000 (PEG-8000). The top Ni-layer morphology of these samples was characterized by atomic force microscope (AFM). Detailed analysis of the morphological data showed a typical two-dimensional fractal growth pattern in all the three cases. The structural parameters like interface roughness, density and thicknesses of Ni and Cu layers were extracted from neutron reflectivity (NR) study. The order of interface roughness obtained from NR and AFM was found to be quite close. The sample deposited from sulphate–citrate electrolyte was found to have minimum interface roughness. The polarized neutron reflectometry (PNR) measurement showed reduced magnetic moment value (∼0.41 ± 0.01 μ_B) for nickel layers compared to bulk value in all the three samples. The magnetoresistance (MR) of these samples were measured at room temperature. An attempt has been made to explain the observed MR results in terms of granular structure and scattering mechanism involving super-paramagnetic and ferromagnetic particles in these samples.     

Magnetic properties of thin-film Co/Fe/Ni magnetic systems

The magnetic properties of Co/Fe/Ni thin-film structures grown by magnetron sputtering have been studied using magnetooptical techniques. The results of x-ray diffraction measurements showed that all samples possessed a nanocrystalline structure. The magnetization curves and hysteresis loops were measured using the equatorial Kerr effect for two orientations of the external magnetic field. It is established that the Co/Fe/Ni thinfilm structures exhibit a planar magnetic anisotropy. The magnetic behavior of each layer in the initial inhomogeneous Co/Fe/Ni structure is substantially influenced by stray fields of the adjacent layers. This circumstance accounts for the complex shapes of hysteresis loops. The annealing in vacuum at T = 500°C renders Co/Fe/Ni thin-film structures magnetically hard compared to the initial state. The experimental results are explained by certain features of the microstructure of samples.     

铜镍铬镀层的环保型挂具电解退镀工艺

为进一步提高铜镍铬镀层退挂液性能,优选了用于剥离铜镍铬镀层的挂具电解退镀剂主要成分的浓度,在此基础上对促进剂用量和缓蚀剂种类及用量进行了优选,最终确定退镀液的最佳配方:硝酸钠20 g/L,醋酸铵18 g/L,三乙醇胺9 g/L,促进剂TG-1 1.2 g/L,缓蚀剂TG-2 7.2 g/L。以最佳配方制成挂具电解退镀剂产品DW-2,与行业内使用较广的同类产品相比,DW-2具有较快的退挂速度和较小的基体腐蚀率,并且操作简单、易处理,安全环保无污染。     

Magnetic and Structural Properties of Ni/NiO Nanoparticles Prepared Using Nickel Acetate and Polyvinyl Acetate Precursor

Ni/NiO nanoparticles were synthesized using a mixture of nickel acetate and polyvinyl acetate as precursors, followed by heating between 350–450 °C. The prepared samples were investigated using XRD, TEM and SQUID magnetometry. Depending on the heating temperature, the average sizes of Ni and NiO crystallites were found to be in the ranges of 25–37 nm and 10–26 nm, respectively. The analysis of XRD patterns shows that the volume percentage of Ni can be easily controlled by the heating temperature. Magnetization measurements show that the samples consist of ferromagnetic moments which are blocked at low temperatures and a disordered NiO component which causes spin-glass like behavior.     

Microstructure and Magnetic Properties of Soft Magnetic Composites with Silicate Glass Insulation Layers

In this study, a new soft magnetic composite (SMC) material design scheme was put forward. According to this design scheme, SMC with silicate glass insulation layers was prepared by powder metallurgy with nanometer glass powder and micron iron powder. It can be annealed at high temperature for reducing residual stress. The magnetic properties were good. The maximum permeability, saturation magnetic induction, residual magnetic flux density and coercivity were 467, 1.47 T, 1.25 T and 394 A/m, respectively. The core loss versus alternating magnetic field frequency showed linear growth. The core loss was 4.4 W/kg at an induction level of 1 T, 50 Hz.