制备条件和退火对Co／Cu多层膜的巨磁电阻及结构的影响

用射频磁控溅射方法在不同条件下制备了数个系列的Ｃｏ／Ｃｕ多层膜样品，成功地观察到巨磁电阻随Ｃｕ层厚度的振荡行为。对比不同制备条件，发现清洁、较好的背景真空是获得巨磁电阻的关键。真空退火显著地降低了巨磁电阻第一峰的数值，其原因是退火引起的界面状态的微观变化导致相邻Ｃｏ层间的铁磁耦合。然而，对第二峰而言，退火后巨磁电阻值变化较小。用Ｘ－光衍射分析了样品退火后结构的变化

INFLUENCES OF PREPARATION CONDITIONS AND ANNEALING ON MAGNETORESISTANCE AND STRUCTURE IN CO/CU MULTILAYERS

Several series of Co/Cu multilayers were prepared by a RF. magnetron sputtering system under different conditions. X-ray diffraction was used to check the structures of Co/Cu multilayers. Small angle x-ray showed good periodic structure, and large angle x-ray difraction showed Cu <111> texture of the multilayers. Oscillation of giant magnetoresistance (GMR) with the change of the thickness of Cu layers was observed in Co/Cu multilayers deposited under the base pressure of Pa without buffer layer. Three GMR peaks were observed clearly. The value of the first MR ratio peak reached 27% and 51% at room and liquid N2 temperature respectively. It was found that low base pressure had a crucial influence on magnetoresistance. The oxidation of Co/Cu multilayers weakened the antiferromagnetic coupling and resulted in low MR ratio. The other conditions, say, the Ar pressure, the substrates etc. were of secondary importance. Thus, according to our experience, in order to obtain reasonable giant MR ratio, the base pressure should not be higher than Pa. The effect of annealing on the MR ratio was studied in Co/Cu multilayers. Annealing was performed in vacuum with different annealing temperatures. The annealing time was an hour. it was found that annealing in vacuum reduced the value of the 1st peak of GMR significantly. Microscopic change of the state introduced ferromagnetic interlayer coupling between adjacent Co layers by forming ferromagnetic bridges and diminished the 1st GMR peak. The 2nd GMR peak, on the other hand, was not changed much. For these samples with thick Cu sublayers, the MR ratios even became larger after annealing. X-ray diffraction method is used to investigate the degradation of the structure. The intensity of small angle x-ray diffraction of the samples with the first and second MR peaks changed unmonotonously. And large angle x-ray diffraction of the sample showed the occurrence of Cu <200> texture after annealing.