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 '45° 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.