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 anisotrop y of thin ferromagnetic films on strongly paramagnetic substrates that are slightly anisotropic. The film that we consider is composed of the much stu died manganite La0.7Ca0.3MnO3 and the substrate is NdGaO3, a good lattice m atch. Below a Curie temperature T-c of 260 K it was found, using a vibratin g sample magnetometer, that 72 +/-3 nm La0.7Ca0.3MnO3 films grown epitaxial ly by pulsed laser deposition on untwinned orthorhombic NdGaO3 (001) substr ates 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 c ell which is orthorhombic. We attribute an 11 +/-4% loss of the low tempera ture moment to the proximity of the paramagnetic substrate rather than to s tress. It is argued that stress is minimal such that the observed anisotrop y must be magnetocrystalline. Both the reduction in moment and the anisotro py must be taken into account when designing thin film experiments. (C) 200 1 American Institute of Physics.