Soft perpendicular magnetization and spin reorientation transition of Fe films on NiAl(001)

Ultrathin Fe films were deposited on NiAl(001) for studies of their magnetic properties and crystalline structures. Thickness-driven perpendicular to in-plane spin reorientation transition was observed at a thickness of ∼4 monolayers (MLs) at room temperature without structural variation. At less than the critical thickness, the Fe film's easy axis is perpendicular to the surface plane with a small coercive field (H_c ≈ 1 Oe), which was much smaller than that of other systems with perpendicular anisotropy. The Fe/NiAl(001) system revealed an extremely soft perpendicular magnetization. At more than the critical thickness, the easy axis lays in the surface plane. The magnetic anisotropy terms were calculated and discussed through a phenomenological model. The weaker surface anisotropy might be attributed to the reconstructed NiAl(001) surface.