Finding stabilized coercivity in a study of thickness and temperature dependent Co/Ag/Ge(001) ultrathin films

Epitaxial magneto-optical Co/Ag/Ge(001) ultrathin films were investigated at both room temperature and low temperature. Interesting variations in coercivity as a function of thickness and temperature suggest the existance of interfacial exchange interactions. The operative Ag layers required to inhibit intermixing of Co-Ge alloys from the oscillation of coercivity with Ag film thickness were determined. When the Ag film thickness was reduced to the submonolayer range, perpendicular anisotropy was unexpectedly found. Thus unusual phenomenon can be qualitatively discussed in terms of effective magnetic anisotropy by the contribution of reduced Co layers and by surface magnetic anisotropy.     

Structure of ultrathin MgO films on Mo(001)

We have studied the structure of ultrathin MgO films grown on a single crystal Mo(001) surface. Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) were used to investigate the effect of substrate temperature and oxygen partial pressure on the growth and morphology of these films. LEED indicates the growth of (100) films with MgO 〈110〉 directions oriented along 〈100〉 directions of the substrate. Despite the insulating nature of bulk MgO, films up to 25-Å thick are sufficiently conducting to perform STM measurements. STM reveals Mg deposition in an oxygen ambient at substrate temperatures from 300 to 900 K produces uniform films. Films as thick as eight atomic layers typically have only three layers exposed. These films consist of small domains between 20 and 60 Å in diameter. The domain shapes are random and the perimeters show no preferred orientation. In contrast, films grown at temperatures in excess of 1000 K exhibit larger three-dimensional MgO islands (Volmer-Weber growth). Steps on these high temperature films orient preferentially along thermodynamically favored MgO 〈100〉 directions. STM images of films deposited at high temperature exhibit a checkerboard pattern. The dimensions and symmetry of this pattern are consistent with the coincidence arising from the mismatch of the MgO(100) and Mo(001) lattice. Annealing room temperature deposited films results in island coalescence and produces uniform films with domains in excess of 100 Å. The perimeters of these domains are oriented along MgO 〈100〉 directions.     

Magnetic and Structural Properties in Co/Cu/Co Sandwiches with Ni and Cr Buffer Layers

1. IntroductionThe gial magnetoresistance (GMR) effect occursin multilayers of ferromagnet ic / nonmagnet ic met almultilayers and sandwiches[1'2]. Many material systems, such as Fe/Crl'], Co/Cut'l, have exhibited theGMR properties. The saturation field in these multilayers is usually very large due to the strong exchange coupling field between the adjacent magneticlayers. Non-coupled type multilayers consisting of twomagnetic components with different coercive forces,and relatively thick …     

Sorption behaviour of Co(II) and Cu(II) on chitosan in presence of nitrilotriacetic acid

Separation and isolation of radioactive cobalt ((60)Co), one of the main contributors towards the activity build up in nuclear reactors, is essential for radioactive waste volume reduction during nuclear reactor decontamination procedures. In this context, sorption of free and complexed Co(II), Cu(II) and nitrilotriacetic acid (NTA) on the biosorbent, chitosan was studied. A detailed investigation on the role of pH on sorption of Co(II), Cu(II) and NTA was done. Uptake capacities of the metal ions and NTA were measured within pH range of 2.0-7.0. At pH above 5, the NTA uptake capacities were found to be higher in presence of the metal ions than in their absence. Effect of NTA was found to be more pronounced on copper uptake than on cobalt uptake. Significant change in selectivity of chitosan towards metal ion uptake from NTA medium was observed with respect to change in pH. At pH 2.9, the uptake of cobalt was found to be more than that of copper, while the selectivity was reversed at pH 6.0. The respective selectivity coefficient (k(Co/Cu)) values were found to be 2.06 and 0.072.     

Thickness dependent reactivity and coercivity for ultrathin Co/Si(111) films

For Co/Si(111) films thinner than 15 ML, the thickness dependent reactivity and magnetic properties have been systematically studied. As the Co coverage increases, Co adatoms on the Si(111) surface show enhanced chemical reactivity for oxidation due to the change of the chemical state. After the saturation oxygen exposure, oxygen atoms interact with a thick Co layer to form a rougher interface. Complex adsorption kinetics of oxygen in the Co layer is observed. From the depth-profiling measurements for Co layers close to the Co-Si interface, the sputtering rate is enhanced due to that the solid surfaces of Si and Co-Si compounds are resistive against oxidation. The descending of the Kerr intensity by saturation oxygen exposure shows the limited diffusion length of oxygen atoms into the films. The inertness of the Co-Si interface, the reduction of pure cobalt and imperfection introduced by oxygen influence the coercivity of O/Co/Si(111).     

曲折状FeSiB/Cu/FeSiB三层膜结构应力阻抗效应研究

采用磁控溅射法在玻璃基底上制备了曲折状FesiB／cu／FesiB三层膜结构,在1—40MHz范围内研究了FeSiB膜和Cu膜厚度对三层膜结构应力阻抗效应的影响。结果表明：高频下三层膜的应力阻抗效应随着其形变的增加近似线性增加,在自由端弯曲变形1mm、外加电场频率为25MHz时,应力阻抗效应达到-18．3％,在力敏传感器方面具有广阔的应用前景。     

The Study of Half-Metallicity in Zincblende CrBi (001) and VBi (001) Surfaces and CrBi/InSb (001) and VBi/InSb (001) Interfaces

Density functional theory calculations were performed to study the structural, electronic, and magnetic properties of hexagonal NiAs-type, cubic rock salt (RS)-type, and cubic zincblende (ZB)-type CrBi and VBi compounds, free (001) surfaces of ZB CrBi and VBi, and interface of ZB CrBi (001) and VBi (001) with InSb (001). Antiferromagnetic (AFM) NiAs structure was a ground-state structure of bulk CrBi and VBi. The ZB structure of CrBi and VBi was found to be ferromagnetic (FM) half-metals with total moments of 3 B and 2 μ _B per formula unit, respectively. Calculated surface energies in the framework of ab initio atomistic thermodynamics indicated that the Bi-terminated (001) surfaces of CrBi and VBi have the lowest energy over the entire accessible region of chemical potentials with respect to Cr- and V-terminated (001) surfaces. Half-metallic (HM) characteristic was preserved at Cr (001) and V (001) terminations, while half-metallicity disappeared at Bi (001) terminations. Half-metallicity was also retained at CrBi/InSb (001) and VBi/InSb (001) interfaces, introducing ZB CrBi and ZB VBi as promising candidates for possible epitaxial growth on InSb semiconductor substrate in spintronic applications.     

Diffusion-induced step decoration of Co on Ag(001)

We have investigated submonolayers of Co deposited on a Ag(001) surface with ultra low energy ion deposition and a deposition energy ranging from 5 to 30 eV. The sites of nucleation, the island densities and heights were determined with scanning tunneling microscopy. Next to randomly distributed islands on the terraces observed for every deposition energy, preferential nucleation on the upper side of the Ag steps was observed only for 5 and 15 eV. We found that for increasing characteristic length between the islands on a terrace, the number of islands per unit step length increases. This implies that step decoration is related to enhanced diffusion of Co atoms on the Ag surface during nucleation.     

Cu surface segregation in Ni/Cu system

We report experimental evidence of Cu surface segregation in Ni/Cu system, during deposition of Ni film onto Cu substrate at room temperature and during heat treatment in vacuum. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) by Tougaard's analysis results show that surface segregation defeats in competition with increase in Ni thickness and terminates when thickness of Ni increase to more than 4 nm. Surface energy and concentration were calculated using contact angle measurements and the results confirm that segregation reduces the surface energy. Surface segregation during heat treatment at 150-220 °C range as a function of time initially shows linear mass transfer. By solving Fick's equation and taking empirical diffusion coefficient, 125 ± 20 kJ/mol is obtained for activation enthalpy of effective diffusion.     

Cu Diffusion in Co/Cu/TiN Films for Cu Metallization

Some information on how to use in-situ determined diffusion coefficient of Cu to make barrier layer of Cu metallization in ultra large scale integrations （ULSIs） was provided. Diffusion coefficients of Cu in Co at low temperature were determined to analyze Cu migration to Co surface layer. The diffusion depths were analyzed using X-ray photoelectron spectroscopy （XPS） depth profile to investigate the diffusion effect of Cu in Co at different temperatures. The possible pretreatment temperature and time of barrier layer can be predicted according to the diffusion coefficients of Cu in Co.     

Growth, structure and epitaxy of ultrathin NiO films on Ag(001)

NiO ultrathin films have been grown on Ag(001) by Ni deposition in an O₂ atmosphere. The thickness range 5–50 ML has been investigated. X-ray photoelectron spectroscopy has been used to study the stoichiometric composition and chemical purity of the oxide films. We found completely oxidized stoichiometric NiO films. Their contamination has been found to be limited to the topmost layers. Photoelectron diffraction has given information concerning the local crystal structure of the films. The film atomic geometry has been found to be the same independent of thickness in the 0–50 ML range. The films have the expected (001) rock-salt structure with the same in plane orientation as the Ag(001) substrate. Specular X-ray reflectivity has allowed a very accurate thickness evaluation and has given information on the width of the density gradients at the film–substrate and vacuum–film interfaces, found to be of the order of a few atomic layers.     

Structure and magnetic properties of LiMVO4 (M = Co,Ni, Cu) spinels

The two-dimensional antiferromagnetic correlations found for LiCuVO₄ below 30 K have been explained by considering the ordered distribution of lithium and copper in the octahedral sites.     

锂离子电池Li3-xMx N(M:Co,Ni,Cu)系列负极材料研究进展

Li3-xMxN(M:Co,Ni,Cu)具有首次脱锂容量大,良好的充放电可逆性等优点,是制备锂离子电池负极的优良材料.本文介绍了此系列材料的制备方法、结构、特性及其性能.     

Structural characterization of a Cu/MgO(001) interface using CS-corrected HRTEM

Epitaxial Cu(001) layers were deposited on MgO(001) substrates by magnetron sputtering and the atomic structure of the Cu-MgO interface was characterized by spherical aberration (C_S)-corrected high-resolution transmission electron microscopy (HRTEM). The interface structure and the misfit dislocation network were determined by imaging in both the <100> and <110> directions. The dislocation network was found to lie along the <100> directions with a Burgers vector of ½ a_Cu <100> deduced from HRTEM images and geometrical phase analysis. The dislocations do not fully accommodate the lattice mismatch, yielding residual stress at the interface and an elongation of the Cu lattice along the [001] direction.     

Giant Magnetoresistance Effect of [bcc-Fe(M)/Cu](M=Co,Ni) Multilayers

1. IlltroductionGiant magnetoresistance (GMR) effect of metallic multilayers has been widely investigated after thefinding by Baibich et al.11], as a new phenomenon tobreak through the memory density in ultra high density magnetic recording, high sensitivity in magnetichead, and so on. Metallic multilsyers of 3d transition elements could be classified into three groups of[bee/bcc], [fee/fccl and [bee/fcc] from the standpointof combination of crystal structure of constituting elements of metal…     

Corrosion behaviour and magnetic properties of melt-spun Nd-(Fe·Co·Ni)-B-(Al·Ti) ribbons

The corrosion behaviour of melt-spun Nd-Fe-B alloy ribbons in which Fe was replaced with Co and Ni and small quantities of Al and Ti added was investigated from the viewpoint of anodic corrosion, Although the addition of Ni degraded the magnetic properties of melt-spun ribbons, it improved corrosion resistance. According to EDXS and AES analyses, the corrosion products on the surface of Ni-free ribbons consisted of Nd and Fe oxides, but the Nd oxide corrosion product almost disappeared in the Ni-added samples. Also, the degradation of magnetic properties after the corrosion test was suppressed by the addition of Ni.From these results, it was thought that the improvement of corrosion resistance and the smaller degradation of magnetic properties of Nd-(Fe·Co·Ni)-B-(Al·Ti) ribbons after the corrosion test were associated with the suppressed dissolution of the Nd-rich phase at the grain boundaries.The oxidation of Ni-added melt-spun ribbons also showed similar characteristics and behaviour to the corrosion test in the morphologies of the ribbon surface and magnetic properties after the oxidation test.     

Sm（Co、Cu）_5和Sm_2（Co、Cu）_（17）的相平衡热力学分析

本文首先导出三元系中固溶体α与线性化合物。两相平衡方程及两平行线性化合物θ和两相平衡方程．利用Ｃｏ—Ｃｕ—Ｓｍ系１２５０℃时α（Ｃｏ、Ｃｕ、Ｓｍ）与θ—Ｓｍ２（Ｃｏ、Ｃｕ）１７·θ一Ｓｍ２（Ｃｏ、Ｃｕ）１７与—Ｓｍ（Ｃｏ、Ｃｕ）５两相平衡成分数据及Ｃｏ—Ｃｕ系中提取的Ｆ、Ｃ、Ｃ固溶体α（Ｃｏ、Ｃｕ）的热力学数据．分别求出Ｓｍ２（Ｃｏ、Ｃｕ）１７和Ｓｍ（Ｃｏ、Ｃｕ）５中Ｃｏ和Ｃｕ的交互作用参数Ｉθ＝５３４０Ｃａｌ／ｇ、ａｔ和Ｉθ＝５４３９Ｃａｌ／ｇ、ａｔ．并指出了含有Ｓｍ２（Ｃｏ、Ｃｕ）１７或Ｓｍ（Ｃｏ、Ｃｕ）５相的合金利用调幅分解以提高硬磁性的可能性和适用范围．     

Synthesis of Cu3(PO4)2 · H2O based solid solutions through Co or Ni substitution for Cu

New substitutional solid solutions have been synthesized: (Cu_{1 ? x} Co_x)₃(PO₄)₂ · H₂O (0 < x ≤ 0.20), (Cu_{1 ? x} Ni_x)₃(PO₄)₂ · H₂O (0 < x ≤ 0.12), and (Cu_{1 ? y} Co_y)₃(PO₄)₂ · H₂O (0.55 ≤ y ≤ 0.65). The first two solid solutions are isostructural with Cu₃(PO₄)₂ · H₂O (monoclinic symmetry, sp. gr. C2/c); the third solid solution also has a monoclinic structure, which is a Cu₃(PO₄)₂ · H₂O related superstructure. The lattice parameter b of (Cu_{1 ? y} Co_y)₃(PO₄)₂ · H₂O (0.55 ≤ y ≤ 0.65) is almost twice that of (Cu_{1 ? x} Co_x)₃(PO₄)₂ · H₂O (0 < x ≤ 0.20), while their a and c parameters differ little. The solid solutions have been characterized by chemical analysis, x-ray diffraction, IR spectroscopy, and thermal analysis.