Microstructure and magnetic properties of sputtered Fe-Pt thin films

The characterization of rf magnetron-sputtered Fe-Pt thin films at various compositions (Pt = 15, 24, 46 and 78 at%) is reported. X-ray diffraction studies on annealed Fe-46%Pt thin films at 600 deg C revealed an ordered L10 γ2-FePt phase with fct structure whereas annealed Fe-24%Pt and Fe-78%Pt films exhibited ordered γ1-Fe3 Pt and γ3-FePt3 phases, respectively. The effects of argon quenching and rapid thermal annealing (RTA) on the structural and magnetic properties are investigated. When the films are annealed at 600 deg C for 1 h and then quenched to room temperature in argon gas, ordered γ2-FePt with L10 phase is obtained. Argon-quenched and rapid thermal annealed films exhibit microtwins in scanning electron microscopy analysis. The appearance of microtwins may be attributed to the planar defects developed in the FePt films due to the release of elastic strain during annealing. The saturation magnetization is found to increase with ferrous content in the films. Argon-quenched Fe-46%Pt films exhibited larger saturation magnetization than RTA-processed films. The large value of saturation magnetization obtained from M- H hysteresis indicates the predominant existence of the hard fct γ2-FePt phase. The combined effects of twins, long-range order and the hard γ2-FePt phase on the magnetic properties are discussed