Granular nanostructures and magnetic characteristics of FePt-TiO2/FePt-C stacked granular films

To realize a granular film composed of L10-FePt grains with high uniaxial magnetic anisotropy energy, Ku, and segregants for heat-assisted magnetic recording, the FePt-TiO2/FePt-C stacked film was investigated. The FePt-TiO2/FePt-C stacked film has well-isolated granular structure with average grain size of 6.7 nm because the FePt-TiO2 film follows the FePt-C template film in microstructural growth. However, the Ku value is quite low for total thickness of 9 nm: 5 × 106 erg/cm3. Exploration of the thickness dependence of L10-FePt(001) peaks in XRD spectra and cross-sectional TEM images suggest that degradation of the L10 ordering appears near the middle of the FePt-TiO2 layer. The EDX-STEM mapping reveals that Ti atoms exist within the FePt grains in addition to the grain boundary. This indicates the possibility that TiO2 tends to be incorporated into the FePt grains and that it prevents L10-ordering of the FePt grains along the normal-to-plane direction