Bit Patterned Structure Fabricated by Kr $^{+}$ Ion Irradiation onto MnBiCu Films

Mn₅₄Bi₂₄Cu₂₁ (15 nm) films with a perpendicular anisotropy were prepared by annealing the sputtered MnCu/Bi multilayer at a temperature of 350 °C. The MnBiCu film had a rather flat surface of R_a = 1.1 nm, and uniform maze domain was observed before the ion irradiation. The magnetization and coercivity of the MnBiCu film were confirmed to disappear after a low Kr⁺ ion dose of 5 ×10¹³ ions/cm². Bit patterned media (BPM) using the MnBiCu (15 nm) films were fabricated by 30 kV Kr⁺ ion irradiation through electron beam lithography-made resist masks. The surface of the ion-irradiation BPM was almost identical to that of the as-annealed film. The magnetization processes of the bit patterned media were investigated by magnetic force microscope observations after application of the magnetic field. The patterned MnBiCu bits with a size ranging from 500 × 500 nm to 300 × 300 nm have a multidomain state and their magnetization reversals undergo nucleations of the reversed domain and wall propagation. By decreasing the bit size of the patterned MnBiCu, the average switching field H_sf of the bits was increased. This means that the exchange coupling between the patterned bits and the bit edge damage were negligibly small, and shows the possibility of high density ion irradiated planar bit patterned media.