Magnetic properties and microstructures of Fe-Pt thin films sputter deposited under partial nitrogen gas flow

Continuous Fe100-x Ptx thin films (x=44, 50, 56, 60, and 65) with a thickness of around 80 nm were prepared by dc magnetron sputtering under a mixture of argon and nitrogen gases. The maximum coercivity was obtained at the Fe56 Pt44 off-stoichiometric composition after postannealing for L 10 ordering. For the equiatomic and Pt-rich films, partial nitrogen flow during sputtering deteriorated the in-plane coercivity of the postannealed samples due to conglomeration of smaller grains and the presence of L 12 Fe Pt3 phase. After postannealing for L 10 ordering, the Fe-rich films grown in argon and mixture of argon and nitrogen atmospheres are both composed of L 10 fct phase only, and the enhancement of the degree of order and strong preferential in-plane alignment of the c axis in the presence of nitrogen causes in-plane coercivity increase. By introducing nitrogen during sputtering, an in-plane coercivity of 1303 kAm (16.4 kOe) was obtained for the continuous Fe56 Pt44 thin film annealed at 700 °C.