Addition of a small amount of Pt greatly enhances the magnetic hardness of Co films. By combining this hard Co94.5Pt5.5 film with a soft permalloy film, we prepared Co-Pt/Cu/permalloy sandwiches, and investigated their magnetoresistance and the interlayer coupling between the two magnetic layers. The sandwiches exhibited large magnetoresistance of up to 4.4% without any buffer underlayers, although the magnetization reversal field of the permalloy layer was increased due to the ferromagnetic interlayer coupling with a Со-Pt layer. In order to reduce the coupling, the interfacial roughness in the sandwiches and the magnetization fluctuations in each magnetic layer must be reduced.
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