Giant magnetoresistance in Co/Cu, Co9Fe/Cu, and Co7.5Fe2.5/Cu multilayers

The authors report that giant magnetoresistance (MR) at room temperature up to 52% for a low field change of 0.9 kOe can be attained in (Co₉Fe/Cu)_n, multilayers. A set of (Co_x Fe_1-x/Cu)_n multilayers (x=1.0, 0.9 and 0.75) was prepared by an ion-beam sputter deposition method on MgO(110) single-crystal substrates. The MR ratio was found to be quite sensitive to the argon acceleration voltage (V_B) in ion-beam sputtering and have a maximum around V_B=600 V. In the preparation condition for obtaining maximum MR ratio, strong antiferromagnetic coupling (J) for the Co_xFe_1-x layers via thin Cu layers and the oscillation behavior for this indirect exchange coupling with a 12-A period were observed. It was found that the MR ratio for Co_xFe_1-x multilayers is larger than that for Co/Cu multilayers in the higher Co-concentration range in the Co_xFe_1-x alloy. It was also found that in-plane uniaxial anisotropy (K_u), on the order of 10° erg/c³, was induced when this system was prepared on MgO(110). Giant MR can be induced for a small external field change for film with magnetocrystalline anisotropy. MR curve behavior can be explained by metamagnetic transition when K_u, J , and Zeeman terms are considered