Paramagnetic anisotropy in high-T/sub c/ superconductors

Magnetic alignment of RBa2Cu3O/sub 7-//sub x/ particles results from anisotropy in paramagnetic susceptibility, an anisotropy that differs in sign for different rare earths. Various factors contributing to this anisotropy are discussed, particularly the rare-earth single-ion anisotropy associated with crystal fields and second-order Stevens factors. For R = Eu, the observed anisotropy is consistent with that expected from the crystal-field splitting of J = 1 excited levels