Magnetic anisotropy of ferromagnetic La0.7Sr0.3MnO3 epitaxial thin films: Dependence on temperature and film thickness

The magnetic anisotropy of (001) oriented ${\mathrm{La}}_{\text{0.7}}{\mathrm{Sr}}_{\text{0.3}}{\mathrm{MnO}}_3$ films of thickness $\text{t=7–156\hspace{0.17em}}\mathrm{nm},$ deposited on ${\mathrm{LaAlO}}_3$ substrates, was measured by torque magnetometry in the temperature range $\text{T=10–300\hspace{0.17em}}\mathrm{K}.$ For $\text{t⩾50\hspace{0.17em}}\mathrm{nm}$ and H rotating out of plane the anisotropy $K_u$ agrees well with shape anisotropy. For thinner films, $K_u$ is reduced and its sign is reversed for $\text{t=7\hspace{0.17em}}\mathrm{nm}$ and $\text{T<70\hspace{0.17em}}\mathrm{K};$ this can be explained by a perpendicular anisotropy $K_{\mathrm{u\epsilon }}$ due to lattice strain. The crystal anisotropy constant $K_1$ was determined from the biaxial in-plane anisotropy. At $\text{T=100\hspace{0.17em}}\mathrm{K}$ $K_1$ differed by no more than 50% from the mean value $\text{−8\hspace{0.5em}}{\mathrm{kJ/m}}^3$ in the thickness region investigated. $K_1$ was much less dependent on the thickness t and strain relaxation in the films than $K_{\mathrm{u\epsilon }}.$