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, Hc, of the annealed films has a maximum (¿15.8 kOe) at about equiatomic concentration. The origin of the high Hc is considered to be related to the microtwin structure. It was found that Hc 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.