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

•Effect of Hf underlayer on structure and magnetic properties of FePt films are studied.•Hf underlayer reduces size, narrows the distribution of grains and thus enhances intergrain coupling.•Higher Ta≥600 °C makes Hf–Pt intermetallic compound and thus Fe3Pt phase form.•Good in-plane magnetic property is proper for uses in hard biasing magnet in spintronic devices.

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 L10-ordering is triggered by a 400 °C-annealing. At Ta≥600 °C, Hf–Pt intermetallic compound forms with increasing Ta, which consumes Pt in FePt layer and results in the formation of Fe3Pt phase. The film becomes soft magnetic at Ta=800 °C. The optimized condition of FePt/Hf film is in the Ta range of 500 to 600 °C where the interdiffusion between Hf and FePt layer is not extensive. The value of Hc is 8.9 kOe and Mr is 650–670 emu/cm3. 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.