微晶和纳米晶Ni金属在3 K和300 K下的高场磁电阻
High-field magnetoresistance of microcrystalline and nanocrystalline Ni metal at 3 K and 300 K
摘要：
的磁阻（MR）和磁化等温线进行了研究，以高磁场在T = 3 K和300 K的微晶（$μ$ c）Ni箔对应于块体Ni和纳米晶（NC）Ni箔。在T = 3 K时，对于剩余电阻率比（RRR）为331的$μ$ c-Ni样品，电阻率的场依赖性与先前报道的高纯铁磁体相似，而对于RRR = 9的nc-Ni样品，MR（H）行为与在低温下观察到的低杂质浓度的Ni基合金相似。在磁饱和状态下，电阻率增加与磁场为两个样品在T = 3 K和场的依赖性占主导地位的普通MR由于洛伦兹力作用于电子轨迹。然而，发现$μ$ c-Ni的MR（H）曲线是饱和的，而nc-Ni的MR（H）曲线是不饱和的，这一差异是由它们非常不同的电子平均自由程引起的。在T = 300 K时，两种Ni样品的MR（H）曲线与块体Ni的已知曲线非常相似。磁饱和后，电阻率随磁场的增大而近似线性下降，这是由于热致磁无序随磁场的增大而受到抑制。利用Kohler图分析了两种温度下的MR（H）数据，从Kohler图导出了电阻率各向异性分裂（$Δρ_{AMR}$）和各向异性磁阻（AMR）比。结果表明，在T = 300 K，$ρ(H\rightarrow 0)=ρ(B\rightarrow 0)$由于普通MR的贡献可以忽略不计。在3 K和300 K的两个Ni样品的数据被发现表明，$Δρ_{AMR}$与零场电阻率近似线性标度。这意味着，AMR比不随温度变化显着在任一微观结构状态的Ni。
英文摘要：
The magnetoresistance (MR) and the magnetization isotherms were studied up to high magnetic fields at T = 3 K and 300 K for a microcrystalline ($μ$c) Ni foil corresponding to bulk Ni and for a nanocrystalline (nc) Ni foil. At T = 3 K, for the $μ$c-Ni sample with a residual resistivity ratio (RRR) of 331, the field dependence of the resistivity was similar to what was reported previously for high-purity ferromagnets whereas the MR(H) behavior for the nc-Ni sample with RRR = 9 resembled that what was observed at low temperatures for Ni-based alloys with low impurity concentration. In the magnetically saturated state, the resistivity increased with magnetic field for both samples at T = 3 K and the field dependence was dominated by the ordinary MR due to the Lorentz force acting on the electron trajectories. However, the MR(H) curves were found to be saturating for $μ$c-Ni and non-saturating for nc-Ni, the difference arising from their very different electron mean free paths. At T = 300 K, the MR(H) curves of both Ni samples were very similar to those known for bulk Ni. After magnetic saturation, the resistivity decreased nearly linearly with magnetic field which behavior is due to the suppression of thermally-induced magnetic disorder with increasing magnetic field. The MR(H) data were analyzed at both temperatures with the help of Kohler plots from which the resistivity anisotropy splitting ($Δρ_{AMR}$) and the anisotropic magnetoresistance (AMR) ratio were derived. It was demonstrated that at T = 300 K, $ρ(H\rightarrow 0)=ρ(B\rightarrow 0)$ due to the negligible contribution of the ordinary MR. The data for the two Ni samples at 3 K and 300 K were found to indicate an approximately linear scaling of $Δρ_{AMR}$ with the zero-field resistivity. This implies that the AMR ratio does not vary significantly with temperature in either microstructural state of Ni.
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