Os-doped γ-Fe2O3 thin films having high coercivity and high coercive squareness

Abstract

Sputtered γ‐Fe₂O₃ thin films are attractive for use in high density magnetic recording disk media. This paper reports on remarkable improvements made in magnetic properties for γ‐Fe₂O₃ thin films and their microstructures. We have found that high coercivity and high coercive squareness can be obtained by doping γ‐Fe₂O₃ with a small amount of Os. Os‐doped γ‐Fe₂O₃ films 0.1–0.2 μm thick have been prepared on anodized Al alloy substrates by reactive sputtering of an Fe‐Os target, and successive reduction and oxidization treatments. The coercivity and coercive squareness of the film increase with Os content. A γ‐(Fe_0.948Os_0.052)₂O₃ film exhibits the maximum coercivity of 2100 Oe and high coercive squareness of 0.81. Furthermore, Os doping to the γ‐Fe₂O₃ film brings about field‐induced anisotropy (∼10⁵ erg/cc), resulting from the annealing at 250 °C for 1 h in a magnetic field (7 kOe). This induced anisotropy greatly increases the coercive squareness parallel to the easy axis. A coercive squareness of 0.96 is obtained for the γ‐(Fe_0.948Os_0.052)₂O₃ film after the magnetic annealing. Fine crystallites of about 400 Å in diameter are obtained by Os doping which suppresses grain growth during preparation heat treatments.