Epitaxial strain and magnetic anisotropy in ultrathin Co films on W(110)

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Abstract
The role of epitaxial strain for the anisotropies of ultrathin films is studied experimentally for the case of Co(0001) films on W(110), based on the measurement of anisotropies using torsion oscillation magnetometry combined with measurement of the strain by high-angular-resolution low-energy electron diffraction. Up to a thickness of t=2 nm, the films grow in a state of constant strain, governed by pseudomorphism in the direction ([11¯00]Co∥[11¯0]W), which results in a true volume-type strain anisotropy. Above 2 nm, a relaxation of strain is observed which scales roughly with 1/t and therefore results in an apparently surface-type contribution to strain anisotropy, superimposed on a reduced volume contribution. In-plane and out-of-plane volume and surface-strain anisotropies are calculated from the observed strain. For the four anisotropy constants, their calculated differences between the two regimes above and below 2 nm agree with their differences as determined by magnetometry.