Deterioration in coercivities of Fe-Pt and Co-Pt thin film magnets by ion irradiations

Iron-platinum and cobalt-platinum thin film magnets with thicknesses of 120 nm and 135 nm, respectively are irradiated with 180 keV 20Ne or 2 MeV 4He ions, and in-plane coercivities of the magnets are measured as a function of fluences of the ions. Densities of displaced Fe, Co and Pt atoms are calculated with a TRIM code. It is found that the coercivities are determined by the densities of displaced atoms rather than the kind of ions and incident energies. Resistance of the Co-Pt thin film magnets to irradiation of 2 MeV 4He ions is almost the same as that of the Fe-Pt magnets.