Variations in the magnetic anisotropy properties of epitaxial CrO2 films as a function of thickness -: art. no. 094418

The strain resulting from lattice mismatch has a strong influence on the magnetic anisotropy of epitaxial CrO2 films grown on (100) TiO2 substrates by chemical vapor deposition. Thus the magnetic easy axis at room temperature changes orientation with thickness, switching from the in-plane c-axis ([001]) direction for films thicker than 250 nm to the b-axis ([010]) direction for thinner films (<50 nm). Similarly, over a thickness range, a change of the easy axis direction is observed with lowering temperature. The easy-axis switching characteristics can be understood by a simple model that invokes the competing influence of magnetocrystal line and strain anisotropies with varying degree of strain relaxation. Interestingly, films of intermediate thicknesses (50-250 nm) exhibit double-switching phenomena, corresponding to the easy axis being oriented both along the b and c-axis directions. This unusual switching behavior is considered to result from an inhomogeneous distribution of strain in the films, where a portion of the film remains highly strained while the balance is partially relaxed. With increasing thickness, the switching attributed to the latter increases in magnitude while that from the heavily strained component steadily decreases until it is no longer observable for films thicker than 250 nm.