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

The magnetic anisotropy of (001) oriented La0.7Sr0.3MnO3 films of thickness t=7–156 nm, deposited on LaAlO3 substrates, was measured by torque magnetometry in the temperature range T=10–300 K. For t⩾50 nm and H rotating out of plane the anisotropy Ku agrees well with shape anisotropy. For thinner films, Ku is reduced and its sign is reversed for t=7 nm and T<70 K; this can be explained by a perpendicular anisotropy Kue due to lattice strain. The crystal anisotropy constant K1 was determined from the biaxial in-plane anisotropy. At T=100 K K1 differed by no more than 50% from the mean value −8 kJ/m3 in the thickness region investigated. K1 was much less dependent on the thickness t and strain relaxation in the films than Kue.