Spiral-like continuous spin-reorientation transition of Fe/Ni bilayers on Cu(100)

The magnetic domain microstructure of 0 to 3 monolayers (ML) of Fe on 7.2 and 11 ML Ni/Cu(100) films was studied by spin-polarized low-energy electron microscopy at 300 K. The 11 ML Ni layers showed perpendicular oriented stripe domains of some micrometers in width parallel to the atomic step edges of the Cu(100) substrate, whereas the magnetization of the 7.2 ML Ni film was in a canted state. For both Ni layers, perpendicular oriented domains are stabilized upon Fe deposition up to 2.5 ML Fe without changing the original Ni domain pattern significantly. Between 2.5 and 2.9 ML the domains break up into smaller stripe domains, and the magnetization of the coupled Fe/Ni bilayer continuously rotates within the oppositely oriented magnetic stripe domains into the film plane by an in-plane 74degrees spiral-like motion. At 2.9 ML Fe large (10 mum) in-plane magnetic domains appear. From the critical Fe thickness of 2.7+/-0.2 ML we find that the Fe/Ni interface magnetic anisotropy is K-2,Ni-Fe(S)=-93 mueV/atom favoring an in-plane easy axis.