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.