Magnetic anisotropy of thin film La0.7Ca0.3MnO3 on untwinned paramagnetic NdGaO3 (001)

We describe in detail a method by which to establish the magnetic anisotropy of thin ferromagnetic films on strongly paramagnetic substrates that are slightly anisotropic. The film that we consider is composed of the much studied manganite La0.7Ca0.3MnO3 and the substrate is NdGaO3, a good lattice match. Below a Curie temperature T-c of 260 K it was found, using a vibrating sample magnetometer, that 72 +/-3 nm La0.7Ca0.3MnO3 films grown epitaxially by pulsed laser deposition on untwinned orthorhombic NdGaO3 (001) substrates exhibit uniaxial anisotropy with K=(3.6 +/-0.1)x10(5) erg cm(-3). The easy direction is along [110] of the pseudocubic unit cell, i.e., diagonal to the O-Mn-O bond directions and parallel to the side of the actual unit cell which is orthorhombic. We attribute an 11 +/-4% loss of the low temperature moment to the proximity of the paramagnetic substrate rather than to stress. It is argued that stress is minimal such that the observed anisotropy must be magnetocrystalline. Both the reduction in moment and the anisotropy must be taken into account when designing thin film experiments. (C) 2001 American Institute of Physics.