Theory of high-symmetry tetramer single molecule magnets

We present a microscopic theory of single molecule magnets. From our exact single-ion spin matrix elements for four arbitrary spins, we study the single-ion anisotropy of equal spins exhibiting T d , D 2 d , or C 4 v molecular group symmetry. Each group generates site-dependent single-ion anisotropy. For weak anisotropy, accurate Hartree expressions for the magnetization, specific heat, electron paramagnetic resonance (EPR) absorption and inelastic neutron scattering cross-section are given. For D 2 d , azimuthal single-ion anisotropy leads to the observed Ni 4 EPR splittings.