title: Most spin-1/2 transition-metal ions do have single ion anisotropy.
abstract: The cause for the preferred spin orientation in magnetic systems containing spin-1/2 transition-metal ions was explored by studying the origin of the easy-plane anisotropy of the spin-1/2 Cu(2+) ions in CuCl2·2H2O, LiCuVO4, CuCl2, and CuBr2 on the basis of density functional theory and magnetic dipole-dipole energy calculations as well as a perturbation theory treatment of the spin-orbit coupling. We find that the spin orientation observed for these spin-1/2 ions is not caused by their anisotropic spin exchange interactions, nor by their magnetic dipole-dipole interactions, but by the spin-orbit coupling associated with their crystal-field split d-states. Our study also predicts in-plane anisotropy for the Cu(2+) ions of Bi2CuO4 and Li2CuO2. The results of our investigations dispel the mistaken belief that magnetic systems with spin-1/2 ions have no magnetic anisotropy induced by spin-orbit coupling.
authors.affiliation: Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, USA.
authors.forename: Jia
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Chemistry and Research Institute for Basic Sciences, Kyung Hee University, Seoul 130-701, South Korea.
authors.forename: Hyun-Joo
authors.initials: HJ
authors.lastname: Koo
authors.affiliation: Key Laboratory of Computational Physical Sciences (Ministry of Education), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China.
authors.forename: Hongjun
authors.initials: H
authors.lastname: Xiang
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: Reinhard K
authors.initials: RK
authors.lastname: Kremer
authors.affiliation: Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, USA.
authors.forename: Myung-Hwan
authors.initials: MH
authors.lastname: Whangbo