ＣＰＰ‐ＧＭＲおよび鏡面散乱効果によるＧＭＲ効果の高性能化

Abstract

A CPP (Current perpendicular to Plane)-GMR and a specular reflection effect have investigated for an improvement of GMR effect. Structures of films for CPP-GMR were Si/Cu(30nm)/Ta(5nm)/NiFe/CoFe/Cu/CoFe/IrMn/Ta/SiO2(20nm)/AlO(150nm)/Al(200nm) spin valve. The samples were prepared by RF/DC magnetron sputtering system with 10 cathodes. The GMR size is a few mm square. A contact hole was fabricated in a SiO2 layer using Ion milling and Photo lithography technique. A size of holes which were observed by SEM was much smaller than that of mask. Although the resistance of samples decreased with increasing the thickness of an under electrode, the GMR effect was not obtained. Therefore, the samples have the under electrode of 30 nm thick and their resistance is a few Ω. When the Cu layer thickness between two magnetic layers was varied, the change of resistance had a maximum value at 5 nm. AΔR(A is the size of the contact hole, which is regarded as the element area, and ΔR is the change of resistance.) was calculated 0.7 mΩμm2 from the dependence of the relationship between the resistance change and the inverse of A. The resistance change increased with increasing a pinned layer thickness and had a peak value with increasing a free layer thickness. For the total magnetic layer thickness, the resistivity change was obtained the maximum value at 14 nm thick. The specular reflection effect was also investigated for the improvement of the MR ratio. The thin oxidation layer prepared in the pined CoFe layer using a natural oxidation technique. When the CoFe layer was oxidized at the pressure of 0.026 and 0.065 Pa for about 5 minutes, MR ratio increased from 3.5 % to 6 %. The exchange coupling field between the antiferromagnetic layer and the pined layer did not decreased in this conditions.