Resistivity and temperature coefficient of resistance of chromium-copper alloy films

Measurements of electrical resistivity and the temperature coefficient of resistance of vacuum deposited chromium—copper alloy films are reported. The mean freepath of the conduction electrons calculated from resistivity data and TCR data is 37.6 and 36.3 nm, respectively. The resistivity and TCR of an infinitely thick film have been computed to be 3.83 μΩcm and 2.886 × 10^?3° C^?1, respectively. The experimental data can be satisfactorily explained on the basis of Fuchs-Sondheimer theory assuming a total diffuse scattering.     

Extraordinary Hall effect in nanoscale nickel films

The extraordinary Hall effect was studied in 1 to 10nm thick nickel films prepared by radio-frequency diode sputtering (plasma) and electron-beam evaporation of Ni. The Hall resistance, R_H, does not reach saturation in fields up to 0.5 T in films that are not uniform while for uniform films, R_H saturates at 0.3 T. The films prepared by plasma sputtering showed a jump-like behavior of the extraordinary Hall coefficient, R_S, that is due to the presence of two phases—tetragonal (nonmagnetic) and face-centered cubic(fcc) (magnetic)—in the initial growth stage and subsequent phase transition of the tetragonal lattice to fcc at a film thickness of about 4 nm around which the extraordinary Hall coefficient R_S increases abruptly reaching its maximum. The films prepared by electron-beam evaporation consist only of the fcc phase and have a dome-like R_S dependence on film thickness.     

铬青铜与不锈钢瞬间液相扩散焊接界面行为

为了掌握铜合金与不锈钢的连接机理,为工程应用提供技术指导,对铬青铜和不锈钢异种材料扩散焊接进行了研究,对不同厚度的银、铜镀层在不同焊接条件(焊接温度和时间)下的试验进行了分析,利用金相显微镜、扫描电镜以及能谱分析仪分别研究了宏观爆破压力和微观组织结构对焊接质量的影响,对焊接过程发生的冶金结合机理和元素的扩散形式进行了探讨.结果表明,将银、铜镀层的厚度控制在一定范围内,选取950～970℃保温15～60min,焊缝强度可以达到150MPa以上,界面没有脆性相产生.焊缝界面主要表现为铜的扩散、银的反应扩散及TLP过程、银的熔态扩散、铬的聚集析出、镍的网状析出以及柯肯达尔(Kirken-dall)效应等微观特征.     

Electrical conduction and ordinary Hall effect in thin nickel films

A new interpretation is proposed for the size effects in the electrical resistivity of thin nickel films and in the temperature coefficient of resistivity, starting from theoretical equations, recently published. The size effect in the ordinary Hall coefficient is satisfactorily interpreted in the framework of a polycrystalline model; the agreement is questionable in the framework of a columnar model and the assumption of polycrystalline structure I retained.     

Observation of unconventional anomalous Hall effect in epitaxial CrTe thin films

We have studied the magnetic and electrical transport properties of epitaxial NiAs-type CrTe thin films grown on SrTiO₃(111) substrates. Unlike rectangle hysteresis loops obtained from magnetic measurements, we have identified intriguing extra bump/dip features from anomalous Hall experiments on the films with thicknesses less than 12 nm. This observed Hall anomaly is phenomenologically consistent with the occurrence of a topological Hall effect(THE) in chiral magnets with a skyrmion phase. Furthermore, the THE contribution can be tuned by the film thickness, showing the key contribution of asymmetric interfaces in stabilizing Néel-type skyrmions. Our work demonstrates that a CrTe thin film on SrTiO₃(111) substrates is a good material candidate for studying real-space topological transport.

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Theoretical analysis of the Hall effect in thin polycrystalline metallic films

In polycrystalline films where three types of scattering processes (background, grainboundaries and external surfaces scatterings) are taking place at the same time an effective relaxation time is defined in the light of a three-dimensional model of grain-boundaries. Analytical expressions for the Hall coefficient and conductivity in thin polycrystalline metallic films subjected to a transverse magnetic field are then derived by using the Boltzmann transport equation. Previously published data can be theoretically interpreted in terms of the proposed model.     

Size effect in the low-field Hall coefficient of single-crystal copper films

Measurements of the low-field Hall coefficientR _H of single-crystal copper films were made at 4.2 K by the use of a SQUID. The surface normaln of the samples was directed in the [100], [110], and [111] directions and the ratio of the thickness to the mean free path ranged from 0.1 to 0.7. It is found that the effect of surface scattering causesR _H to decrease whenn [100], whereas it causesR _H to increase whenn [110] and [111]. This behavior is interpreted in terms of the geometrical characteristics of the Fermi surface.     

Theoretical analysis of the transverse Hall effect in thin monocrystalline films

The transverse Hall coefficient of thin monocrystalline filmsR _HF is derived from the recently presented bidimensional conduction model by introducing a term in the Boltzmann equation representing the effective mean free path. Numerical evaluations ofR _HF show that the size effect inR _HF is less marked than that in resistivity and is much more sensitive to grain-boundary scattering than it is to external-surface scattering. Good agreement with the results from the previous experiments of several authors is found.     

Hall coefficient in vacuum-deposited copper films

The dependence of the Hall coefficient R_H of vacuum-deposited copper films of thickness, temperature and time was investigated by in situ observation. R_H values were found to be larger than the bulk value and a thickness dependence could hardly be observed down to 100 Å. The temperature dependence was appreciably larger than for bulk material, indicating the existence of the size effect predicted by Sondheimer. R_H for very thin films (below 100 Å) left in the vacuum system at 295°K changed with time, and the change was ascribed to the annihilation of lattice defects in the films.     

Solute segregation effect on grain boundary migration and Hall–Petch relationship in CrMnFeCoNi high-entropy alloy

Homogenisation has been used to eliminate solute segregation of CrMnFeCoNi high-entropy alloys (HEAs) before thermomechanical processing. To overcome the deficiencies caused by high-temperature homogenisation, we cancelled the homogenisation and studied the solute segregation feature and its effect on the grain growth and the mechanical property. The HEA forms equiaxed grains with the solute segregation in the range of tens of micrometres after cold rolling and recrystallisation. The grain growth in recrystallisation still abides by the classical grain growth kinetics, but with a higher power index of 3.33 and activation energy of 392.4?kJ?mol^?1 than those of the homogenised HEA, indicating a solute-drag effect. The relationship between the yield stress and grain size follows the Hall–Petch dependence with a higher intrinsic strength.