Competition between in-plane and out-of-plane magnetization in exchange-coupled magnetic films

The coupling between a Co layer with in-plane easy axis of magnetization and a Ni layer with out-of-plane easy axis across a nonmagnetic Cu spacer layer was studied by layer-resolved magnetic imaging. Photoelectron emission microscopy and magnetic circular dichroism in soft x-ray absorption as the magnetic contrast mechanism were used for the domain imaging. Crossed, wedge-shaped epitaxial Co and Cu layers of 3.5-5.7 atomic monolayers (ML) Co and 2.5-4.1 ML Cu were deposited onto 15 ML Ni/Cu(001). The competition between ferromagnetic interlayer coupling and the magnetic uniaxial anisotropies of the two magnetic layers leads to a noncollinear magnetization configuration at Cu thicknesses above 3.1 ML. The Ni magnetization is thereby in a canted state, whereas the Co magnetization is nearly in plane. The canting angle of the Ni magnetization can be tuned between the surface normal and approximate to45degrees by adjusting the Cu thickness. At a Cu thickness of approximately 3.1 ML a transition to a collinear in-plane configuration at lower Cu thicknesses is observed. This can be explained by a phenomenological expression including the fourth-order anisotropy of the Ni layer.