R&D: Blocking Phenomenon of Hard/Soft Bilayer L10–FePt Grains in Granular Film

IEEE Transactions on Magnetics has published an article written by Daiki Isurugi, Takashi Saito, Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, 6–6–05, Aoba, Aramaki, Aoba–ku, Sendai, Japan, Kim Kong Tham,Tanaka Kikinzoku Kogyo K. K, Tsukuba, Japan, Tomoyuki Ogawa, Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, 6–6–05, Aoba, Aramaki, Aoba–ku, Sendai, Japan, Yoichiro Tanaka, Simon John Greaves, Research Institute of Electrical Communication, Tohoku University, Sendai, Miyagi, Japan, and Shin Saito, Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, 6–6–05, Aoba, Aramaki, Aoba–ku, Sendai, Japan.

Abstract: “L1 ₀ –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, 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 _sw ) increases steeply near the Curie temperature ( TC) 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 _sw near the TC , which means enhancement of robustness against thermal field in random direction. These findings are useful for the design of cap-layer for HAMR media to realize the high spatial resolution.“