Giant magnetoresistance effect of spin valve Co/Pd/Co/NiO

Abstract

The possibility of the giant magnetoresistive (GMR) effect of Co/Pd multilayer was studied based on the prediction of the first principle band calculation. Anti-parallel magnetization configuration was achieved by fabricating spin valve structure, although the parallel magnetization is stable in the Co/Pd multilayer. Spin valve structures of Co/Pd/Co/NiO and Co/Cu/Co/NiO were fabricated on the glass substrate by dual ion beam sputtering. Anti-ferromagnetic NiO films were prepared at room temperature by oxygen reactive sputtering. The metal layers were deposited on the oxide layer subsequently. It is found that there exist a hexagonal phase and well-known cubic phase of NiO by analyzing XRD pattern. The exchange field of Cu/Co/hexagonal-NiO trilayer is larger than that of Cu/Co/cubic-NiO trilayer. The increase of the exchange field is proportional to the relative oxygen concentration. The GMR effect appeared in spin valve structure of Co/Pd/Co/hexagonal-NiO above critical Pd thickness, although GMR ratio is not so large. Anti-parallel magnetization configuration induced by a strong exchange field from NiO leads the GMR effect in the Co/Pd.