Ion Irradiation for Planar Patterning of Magnetic Materials

Kr+ ion dose dependence of the magnetic properties of MnGa films and the fabrication of planar-patterned MnGa films by the local ion irradiation technique were reviewed. The magnetization and perpendicular anisotropy of the MnGa vanished at an ion dose of 1 x 10(14) ions/cm(2) due to the phase change of the MnGa from ferromagnetic L1(0) to paramagnetic A1 phase. The average switching field H-sw of the planar-patterned MnGa increased with decreasing the bit size, implying low bit edge damage in the patterned MnGa, whereas a rather large switching field distribution (SFD) of 25% was confirmed for a bit size of similar to 40 nm. Time resolved magneto-optical Kerr effect measurements revealed that as-prepared MnGa exhibits an effective anisotropy field H-keff = 20 kOe, its distribution H-keff = 200 Oe, and Gilbert damping = 0.008. The ion-irradiated MnGa films exhibited larger H-keff = 22-23 kOe than that of the MnGa before the ion dose. Thus, ion irradiation does not decrease the perpendicular anisotropy, which suggests a small bit edge in the patterned MnGa. H-keff increased from 0.2 kOe to 3 kOe, whereas the length of disorder in the film decreased from 10 nm to 3 nm by ion irradiation.