Magnetic anisotropy in La_(0.7)(Sr,Ca)_(0.3)MnO_3 epitaxial thin films and crystals

摘要

The biaxial and uniaxial magnetic anisotropies of epitaxial { 100} oriented La_(0.7)(Sr,Ca)_(0.3)MnO_3 films on different substrates and of a sphere-shaped single crystal were measured by torque magnetometry at temperatures ranging from T = 20K to room temperature. In the films the biaxial anisotropy with easy axes <110> dominates and is described by a cubic crystal anisotropy constant ranging up to K_1 approxapprox -10~4J/m~3. The uniaxial anisotropy was | K_U | <= 10~3 J/m~3 and is explained by anisotropic stress. In the single crystal the main anisotropy is uniaxial with a hard axis parallel to [ 111], and with an anisotropy constant K_R up to 10~4J/m~3. K_R was measured in different planes and explained by the rhombohedral lattice distortion. The biaxial anisotropy in the crystal (K_1 = -10~3 J/m~3 at T = 100K) was smaller than in the films. Differences between film and single crystalline behaviour are discussed in terms of crystal structure and lattice constriction.