Fabrication and high‐resolution electron microscopy study of FePt L10/A1 graded exchange spring media

We have prepared FePt L10/A1 exchange spring graded media by controlling deposition temperature. The performance of the media was determined by the deposition conditions, particularly the cooling rate. By varying the deposition conditions a coercivity of 4.0 kOe was achieved without loss in remanent magnetization, the value corresponds to 88% reduction compared with that of FePt L10 single phase (32.2 kOe). High-resolution transmission electron microscopy (HRTEM) investigations have revealed that this drastic coercivity reduction originates from the unique microstructure of the specimens: coexistence of the L10 and A1 phases at the interphase boundary. In this region the two phases are dispersed one into another like inclusions in a matrix. Finally, the role of the complicated phase boundary on switching field reduction was discussed using micromagnetic simulations.