Structural transition from L1 phase to A1 phase in FePt films caused by ion irradiation

Abstract

The effect of ion irradiation (B+,Cr+,Ga+, and Nb+) on the crystalline structure and magnetic properties of L10 (face-centered tetragonal structure) FePt films was investigated. Irradiating with Cr+,Ga+, and Nb+ ions of less than 1 at. % (1.6×1015ions∕cm2) dose yielded an almost ideal structural transition from the L10 to A1 (face-centered cubic structure) phase withoutdamage to the surface of the film. This structural transition was accompanied by a change in magnetic properties from a hard magnet with a coercivity Hc of ∼7kOe to a soft magnet with Hc<1kOe. A two-dimensional pattern composed of hard magnetic L10 and soft magnetic A1 phases was fabricated by using a focused Ga+ ion beam.