Control of Magnetic Properties of MnGa films by Kr $^{+}$ Ion Irradiation for Application to Bit Patterned Media

(001) oriented L1₀ phase MnGa films were grown on Cr (20 nm)/MgO(001) substrate, and Kr⁺ ion irradiation on the MnGa films was carried out to control their magnetic properties. Highly ordered MnGa films were obtained at a relatively low temperature of 400°C, and the film exhibited the saturation magnetization M_s of 450 emu/cc and uniaxial anisotropy K_u of ~7 × 10⁶ erg/cc before the irradiation. The M_s and K_u gradually decreased with the ion dose and became zero at the dose of 1 × 10¹⁴ ions/cm². While coercivity H_c of the MnGa showed a slight increase up to the dose of 1 × 10¹³ ions/cm² and decreased abruptly with further increase of the ion dose. Ion beam patterned MnGa film with pitch sizes down to 80 nm was fabricated by the ion irradiation through the micro-fabricated resist masks. Magnetically patterned but topologically flat MnGa film was successfully fabricated, which suggests the practical application of the MnGa films to high-density planer bit patterned media.