Effects of ion-beam irradiation on the L1\u3csub\u3e0\u3c/sub\u3e phase transformation and their magnetic properties of FePt and PtMn films (Invited)

In this paper, we illustrate how to modify the structure and magnetic properties of L10 FePt and PtMn films using ion-beam irradiation. Highly ordered L10 FePt and PtMn phases were achieved directly by using 2 MeV He-ion irradiation without conventional post-annealing. A high ion-beam current density (~μA/cm2 ) was used to achieve direct beam heating on samples. This irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered L10 phase. In-plane coercivity of FePt films greater than 5700 Oe could be obtained after disordered FePt films were irradiated with a He-ion dose of 2.4x1016 ions/cm2. The direct ordering of FePt took place by using ion-irradiation heating at a temperature as low as 230 ℃. In PtMn-based spin valves, an L10 PtMn phase, a large exchange field and a high giant magnetoresistance (GMR) ratio (11%) were simultaneously obtained by using He-ion irradiation. On the other hand, Ge-ion and O-ion irradiation completely destroyed the ferromagnetism of FePt and the GMR of PtMn-based spin valves, respectively