Giant magnetoresistance in Co/Cu, Co/sub 9/Fe/Cu, and Co/sub 7.5/Fe/sub 2.5//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 (Co/sub 9/Fe/Cu)/sub n/, multilayers. A set of (Co/sub x/Fe/sub 1-x//Cu)/sub 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/sub B/) in ion-beam sputtering and have a maximum around V/sub B/=600 V. In the preparation condition for obtaining maximum MR ratio, strong antiferromagnetic coupling (J) for the Co/sub x/Fe/sub 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/sub x/Fe/sub 1-x/ multilayers is larger than that for Co/Cu multilayers in the higher Co-concentration range in the Co/sub x/Fe/sub 1-x/ alloy. It was also found that in-plane uniaxial anisotropy (K/sub u/), on the order of 10 degrees erg/c/sup 3/, 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/sub u/, J, and Zeeman terms are considered.<
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