Effects of Pt and Fe underlayers on the microstructure and magnetization reversal of epitaxial FePt films for high areal density magnetic recording

The effects of underlayer on the microstructure and magnetic characterizations of epitaxial FePt films were studied. Enhanced out-of-plane coercivity and ordering were obtained in the Pt-underlayered FePt samples, which may be due to the proper lattice strain from the Pt underlayer. The larger lattice parameter of Pt may enlarge the a axis and reduce the c axis of the L 10 FePt phase and result in low-temperature ordering. However, such an effect does not appear in Fe-underlayered samples because of the smaller lattice parameter and the considerable interdiffusion. The angular dependence coercivity revealed that the dominant reversal mechanism of the FePt films changed from domain-wall motion to rotation, which is caused by the formation of L 10 island structures induced by the Pt underlayer. On the other hand, the Fe-underlayered FePt films showed a broad peak roughly at 45°, implying the tilt of the easy axis about 45° away from the film normal.