Effects of ion-beam irradiation on the L10 phase transformation and their magnetic properties of FePt and PtMn films (Invited)

Abstract

ABSTRACTIon-beam irradiation shows enhancement or degradation of magnetic properties on L10 phase of FePt and PtMn films. A highly ordered L10 FePt phase was directly achieved by using 2 MeV He-ion irradiation without conventional postannealing. The in-plane coercivity greater than 5700 Oe can be obtained after disordered FePt films were irradiated at the beam current of several μA/cm2 with the ion does of 2.4×1016 ions/cm2. The high beam-current-density results in direct beam heating on samples. In addition, the 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 phase. Consequently, the direct ordering of FePt took place by using ion-irradiation heating at temperature as low as 230°C. The comparison has been made on the [Fe/Pt]10/C films by RTA and high current-density He irradiation. Although RTA and ion irradiation both reach high coercivity, ion irradiation seems to suppress the (001) texture, leading to isotropic Hc. Ion-beam irradiation can also be applied to the transformation of PtMn. An ordered PtMn phase, a large exchange field and a high GMR ratio (11%) were obtained in PtMn-based spin valves by using 1.25 μA/cm2 He-ions. On the other hand, Ge-ion and O-ion irradiation completely destroyed the ferromagnetism of FePt and GMR of PtMn-based spin valves, respectively. We propose a novel approach to achieve magnetic patterning by using ion irradiation, which can be applied for patterned media and magnetic sensors.