Reduction of Ordering Temperature of FePt--Al₂O₃ Thin Films by N₂ Addition During Sputtering

We investigate the effect of N₂ addition during sputtering on the microstructure and magnetic properties of FePt--Al₂O₃ thin films. The texture of FePt phase in FePt--Al₂O₃ thin films changes from (111) to a more random orientation by N₂ addition during sputtering. The ordering temperature of FePt phase reduces about 100°C with appropriate N₂ partial pressure. A larger coercivity of 6.0×10⁵A/m is obtained with N₂ partial pressure about 15%. Structural analysis reveals that a small quantity of Fe₃N phase forms during sputtering and the release of N atoms during the post annealing induces a large number of vacancies in the films, which benefits to the transformation of FePt phase from fcc to fct.