Blocking Phenomenon of Hard/Soft Bilayer L10-FePt Grains in Granular Film

L10-FePt grains with structural inhomogeneity in a granular film was investigated, and their blocking phenomenon was simulated. It was confirmed that: 1) structure analysis reveals that both lattice distorted disordered portion at the bottom region near the interface with MgO underlayer and ordered portion at the upper region exist inside one FePt grain in a granular film and 2) simulation of blocking phenomenon for FePt grains with structural inhomogeneity which consists of a hard (order)/soft (disorder) bilayer shows that switching field (
${H}_{\mathbf {sw}}$
) increases steeply near the Curie temperature (
${T}_{C}$
) of the disorder layer with decreasing temperature. To generalize blocking phenomenon of the hard/soft bilayer structure, it was found that matching the Curie temperatures of the hard and soft layers leads to enhancement of
${H}_{\mathbf {sw}}$
near the
${T}_{C}$
, which means enhancement of robustness against thermal field in random direction. These findings are useful for the design of cap-layer for heat-assisted magnetic recording (HAMR) media to realize the high spatial resolution.