Modifications of Structure and Magnetic Properties of MnAl and MnGa Films by Kr+ Ion Irradiation

$L1₀ phase MnGa and MnAl films with (001) orientation were fabricated by magnetron sputtering. Both films were confirmed to exhibit high perpendicular magnetic anisotropies of 7-8× 10⁶ erg/cc and magnetizations of ~450 emu/cc. For the MnGa film, a very flat surface with an average roughness of 0.2 nm was obtained, whereas for the MnAl film, the island growth was confirmed. The X-ray magnetic circular dichroism spectra of these films revealed a significant difference in spectral shape between the perpendicular and inplane magnetized cases. The multiplet peaks appeared in the spectra taken by applying the field normal to the film plane, while such peaks were not clearly seen in the inplane magnetized spectra, possibly owing to the large magnetic anisotropy observed in MnGa and MnAl films. On the other hand, we confirmed a small <;L_z>/2<;S_z>(0.04) and no systematic change of <;L_z>/2<;S_z> between the perpendicular and inplane magnetized cases. Finally, 30 keV Kr⁺ ion irradiation into the films was carried out to modify the magnetic properties of MnGa and MnAl films. In both films, the ion irradiation with a quite low dose of 1×10¹⁴ ions/cm² was confirmed to change the magnetism from ferromagnetic to paramagnetic because of the phase change from L1₀ ordered phase to disordered phase. With the significant variation of the magnetism by a low dose of ion irradiation, MnGa and MnAl are considered to be candidates for planar bit-patterned media fabricated by ion irradiation.