Blocking phenomenon of hard/soft bilayer FePt grains in granular film

The structural inhomogeneity of an L1
0
–FePt grain in a granular film was investigated, and its blocking phenomenon was simulated. It was confirmed that 1) structural analysis reveals that both lattice distorted disordered portion at near the interface with MgO underlayer and ordered potion at the upper region exist inside one FePt grain in a granular film, 2) simulation of blocking phenomenon for FePt grains with structural inhomogeneity, hard (order)/soft (disorder) bilayer grains, shows that switching field (H
sw
) increases steeply near 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 high H
sw
near the T
C
, which means high robustness against thermal field in random direction. These are useful findings for the design of cap-layer media for HAMR to realize the high spatial resolution.