Dependence of Co anisotropy constants on temperature, processing, and underlayer

The dependence of the Co anisotropy constants on the measurement temperature, deposition conditions, and underlayer materials was studied using unicrystal Co(101̄0)/Cr (or NiAl)(112)/Ag(110) films sputter deposited on hydrofluoric acid etched Si(110) substrates. The single, in-plane easy axis orientation in these films allows the direct determination of the anisotropy constants. The anisotropy constants of unicrystal Co films are smaller than those of a bulk Co single crystal, and the temperature dependence of the anisotropy constants is stronger. The K1 value drops by 50% as the temperature is increased from 25 °C to 75 °C, and then becomes negative at 135 °C. This zero-crossing temperature is considerably lower than the 250 °C at which K1 of a bulk Co single crystal decreases to zero. The anisotropy constants also vary with the film preparation substrate temperature. Applying a substrate bias during the Co deposition effectively increases K1 to near bulk material values. Unicrystal Co films grown on NiAl/Ag/HF–Si(110) show smaller K1 as compared to those on Cr underlayers. The addition of a thin Cr intermediate layer on the NiAl underlayer, however, restores K1 to the larger value obtained on Cr/Ag/HF–Si(110).