PHASE FORMATION IN THE FePt/Au/FePt FILMS AND THEIR MAGNETIC PROPERTIES

Abstract

The effect of annealing atmosphere (vacuum, hydrogen) and intermediate Au layer thickness on hard magnetic L1₀ phase formation and magnetic properties of the Fe₅₀Pt₅₀(15 nm)/Au(7.5, 30 nm)/Fe₅₀Pt₅₀(15 nm) films deposited by magnetron sputtering onto SiO₂(100 nm)/Si(001) substrates was studied. Samples were heat-treated in a hydrogen atmosphere under 100 kPa. It was found that a disordered A1-FePt phase formed in as-deposited films. The ordered L1₀-FePt phase forms in the film with an intermediate Au (7.5 nm) layer during annealing in vacuum at 650 °C. Increase in the intermediate Au layer thickness to 30 nm leads to reduction in the ordering temperature to 600 °С. This is promoted by higher compressive stresses in the as-deposited Fe₅₀Pt₅₀ layers with a thicker Au interlayer. In annealing in hydrogen, the A1 → L1₀-FePt phase transition in Fe50Pt50(15 nm)/Au(7.5, 30 nm)/Fe₅₀Pt₅₀(15 nm) films starts at 500 °C regardless of the intermediate Au layer thickness. The Au and FePt axial (111) textures are observed in the films annealed in hydrogen. This is more evident in the films with a thicker Au (30 nm) interlayer. The film with an intermediate Au (30 nm) layer has coercivity of 27.3 kOe after annealing in vacuum at 900 °С. The same coercivity can be achieved by annealing in hydrogen at 700 °С, which is 200 °С lower than after annealing in vacuum due to the introduction of hydrogen into voids of the L1₀-FePt lattice and increase of stress state.