Thickness dependence of magnetic state of Fe thin films grown on Al₂O₃(0001) substrates with an inclined angle

We have investigated the magnetic state of Fe thin films grown on Al2O3(0001) inclined substrates at the Fe thickness range of 5–25 ML (monolayer) (1.0–5.0 nm). For 5 ML Fe films, the magnetic state is superparamagnetic state and the effect of inclination of substrate is negligible. The magnetic state of 10 ML Fe films is in the coexistence of superparamagnetic state and ferromagnetic state, and the effect of inclination of substrate appears but is still a little. In the ferromagnetic region, above Fe thickness of 15 ML, the magnetic easy axis is influenced by the inclination of substrate. Fe thin films grown on the flat substrate have no preferred direction of magnetization in the film plane because of the three equivalent variants of the epitaxial Fe(110) on Al2O3(0001). On the other hand, Fe thin films grown on the inclined substrate have a uniaxial magnetic anisotropy, in which the magnetic easy axis is parallel to the step edge. The strength of uniaxial magnetic anisotropy decreases with increasing Fe thickness. This uniaxial magnetic anisotropy might be derived from the effective demagnetization field due to the magnetic charge distribution at the corrugated surface caused by the steps.