Microstructure and Magnetic Properties of FePt-MO $_{\rm x}$ Granular Films

We have studied the microstructures and magnetic properties of FePt-segregant granular films to achieve an ideal media structure on glass substrates for thermally assisted magnetic recording. Although FePt-C granular films show an excellent in-plane structure, it does not have a good surface roughness. Meanwhile, FePt-SiO₂ granular films have a smooth surface and an interconnected in-plane microstructure. Therefore, to obtain both a surface with a small roughness and well-isolated small columnar grains, we have selected four metal oxides, MO_x (M = Nb, W, Zr and Al) as segregants, which are expected to have a driving force for the phase separation between FePt-C and FePt-SiO₂ based on thermodynamic evaluation. In this paper, we introduce the ground for selecting these materials as segregants and then show the microstructure and magnetic properties of FePt-MO_x granular films.