感生各向异性对溅射Ni_(80)Co_(20)合金膜的磁及磁电阻性能的影响

Influence of magnetic anisotropy on magnetic and AMR of sputtered Ni_(80)Co_(20) alloy film

采用磁控溅射方法，在诱导磁场下制备了一系列不同厚度的 Ｎｉ８０ Ｃｏ２０合金薄膜．并研究了外磁场诱导的面内感生各向异性随薄膜厚度及退火工艺的依赖关系，以及各向异性对样品的磁电阻回线和矫顽力的影响。实验发现，外磁场诱导的面内感生各向异性随薄膜厚度的增加而逐渐减弱。沿面内易轴方向测得的磁电阻回线在矫顽力处具有很尖锐的磁电阻变化峰，因而具有很高的磁电阻灭敏度。沿易轴方向的矫顽力比在难轴方向测得的矫顽力大．两者都随膜厚的增加而增大，其差别随膜厚的增加而减小。样品经４００℃真空退火后，面内感生各向异性基本消失，矫顽力也显著降低．实验还发现，当薄膜厚度小于Ｎｉ８０Ｃｏ２０合金的电子平均自由程（～１５ｎｓ）时．各向异性磁电阻、ρ和ρ／ρ都陡然下降；当Ｄ＞２０ｎｓ时，ρ已基本趋于饱和，而ρ／ρ仍继续增大。以上实验结果对 Ｎｉ８０Ｃｏ２０合金膜在磁记录和磁传感技术方面的应用具有实际意义。

A series of Ni80Co20 alloy films with different thickness were prepared by sputtering under an applied magnetic field. The film thickness dependence of the magnetic and transport properties was studied. It was found that the in-plane uniaxial anisotropy was induced for thinner film and faded for thicker film. For the films with in-plane uniaxial anisotropy the magnetoresistance (MR) curve showed a steep MR change and a high MR sensitivity at the coercive field when applied field H parallel to the in-plane easy axis. The coercive field Hc obtained for H applied parallel to the easy axis was larger than that for H applied perpendicular to the in-plane easy axis, and both of Hc increased with increasing film thickness. The film thickness dependence of Hc can be understood within coercive force theory governed by in-plane anisotropy. The values of He as well as in-plane anisotropy dropped after the samples were annealed at 400℃ in a vacuum. The AMR values of ρ saturated when the film thickness D was around 20nm and decreased abruptly when D <20nm, but ρ/ρ increased continuously with D when D>20nm. Above observations were important in the technique application.