Strain-induced perpendicular magnetic anisotropy in ultrathin Ni films on Cu 3Au(0 0 1)

Abstract

We have investigated magnetism, morphology and structure of nickel films grown on Cu 3Au(0 0 1) to explore the potential of modifying magnetic anisotropies by epitaxial strains. Ultrathin films from the submonolayer region up to 55 monolayers (ML) were grown epitaxially on a Cu 3Au(0 0 1) single crystal. Layer-by-layer growth is observed up to 10 ML. A quantitative analysis of the low-energy electron diffraction (LEED) pattern reveals coherent film growth up to 5 ML. Between 5 and 8 ML the in-plane lattice constant is reduced by 4%, which corresponds to a reduction of the film strain by 70%. This is accompanied by an increase in the interlayer spacing, which is in quantitative agreement with predictions of linear elasticity theory. Kerr measurements show that the films have an in-plane magnetization in the thickness region from 3 to 5 ML and for thicknesses larger than 12 ML. Between 5 and 12 ML a perpendicular anisotropy is observed which is particularly pronounced between 8 and 10 ML. This reorientation of the magnetization direction is caused by the coherency strain in the film.