Microstructure of Sputtered High-Coercive Fe-Pt Alloy Thin Films

Fe-Pt alloy thin films were prepared by the rf-magnetron sputtering method. From X-ray diffraction results and TEM observations, the following results were obtained: (1) the as-deposited films are disordered and consist of micrograins of size roughly 150~200 Å; (2) the annealed films are ordered, with grain sizes about 400~500 Å. A lamellar microstructure, which is considered to be a microtwin structure, was observed within the grains. Magnetization measurements revealed that the coercive force, H
_c
, of the annealed films has a maximum (≈15.8 kOe) at about equiatomic concentration. The origin of the high H
_c
is considered to be related to the microtwin structure. It was found that H
_c
begins to increase at an annealing temperature of 300°C, which means that the ordered phase begins to grow at the same temperature. The magnetization, M, of the annealed films was smaller than that of as-deposited films. The decrease in M near equiatomic composition is ascribed to a change in the magnetic structure.