Effect of Microstructure Refinement on Magnetic Properties of Fe-Pt Thin Films

Fe₅₃Pt₄₇ and Fe₅₈Pt₄₂ thin films with 300 nm in thickness prepared using magnetron sputtering were investigated. The films were deposited on heated glass substrates and annealed at 400degC and 800degC for different time. Single phase FePt films with similar chemical ordering but different substructure size were produced in the two series of samples. The effect of microstructure refinement results in significant enhancement in remanence (M_r) of about 38.1% and 30.8% in the Fe₅₃Pt₄₇ and Fe₅₈Pt₄₂ films, respectively. The energy product, (BH)_max, also showed a large increase of 25% and 72%; the maximum value of the two series of films are 16.2 MGOe and 19.6 MGOe, respectively. The large (BH)_max was found to originate from the enhancement of M _r and steep slope of demagnetization curve at coercive point (alpha). As the theoretical predictions, in an isotropic magnet, the magnetic moments in the transition region of magnetization near grain boundary are easy to be aligned by applied field. In this study, it is found that by increasing the magnetic transition region through microstructure refining, the remanence can be effectively enhanced meanwhile facilitate the collective magnetic reversal. Domain structure confirms that the refinement of microstructure effectively reduces the domain size.