Effect of Hf underlayer on structure and magnetic properties of rapid thermal annealed FePt thin films

摘要

FePt(20 nm) and FePt(20 nm)/Hf(10 nm) thin films prepared on the glass substrates by sputtering and post annealing are studied. For both samples, the as deposited films are disordered and L1_0-ordering is triggered by a 400 ℃-annealing. At T_a ≥ 600 ℃, Hf-Pt intermetallic compound forms with increasing T_a, which consumes Pt in FePt layer and results in the formation of Fe_3Pt phase. The film becomes soft magnetic at Ta = 800 ℃ The optimized condition of FePt/Hf film is in the T_a range of 500 to 600 ℃ where the interdiffusion between Hf and FePt layer is not extensive. The value of H_c is 8.9 kOe and M_r is 650-670 emu/cm~3. Unlike FePt films, the Hf-undelayered samples show significantly reduced out-of-plane remanent and coercivity. The values for both are around 50% smaller than that of the FePt films. Additionally, Hf underlayer markedly reduces the FePt grain size and narrows the distribution, which enhances magnetic intergrain coupling. Good in-plane magnetic properties are preferred for the uses like a hard biasing magnet in a spintronic device.