Superexchange interaction between lanthanide ions. Spin-Hamiltonian calculations for the and superexchange

Abstract

Exchange interaction between two lanthanide or actinide ions of configuration bridged by common diamagnetic ligands is theoretically studied using a modified version of the superexchange theory developed in this paper. Exchange spin Hamiltonians were calculated for the and dimers serving as models of the and - superexchange, respectively. Spin - orbit coupling and crystal field splitting of the configuration (resulting in the ground Kramers doublet and the effective spin of the metal ion), virtual transfers of electrons of the type - - via and valent orbitals of the bridging ligands, and exchange pathways in these dimers are considered in detail. The superexchange is found to be extremely anisotropic and very sensitive to the geometry of the dimer. The spin Hamiltonian of the dimer is , where the exchange parameters are rationalized in terms of and parameters referring, respectively, to the - and - pathways of the electron transfers, , and . The and values are analytically expressed through and overlap integrals, orbital energies and intra-ionic Slater parameters. Exchange interaction between ions in the dimer is described by an antiferromagnetic Ising Hamiltonian , where the z axis connects two metal ions. Unusual magnetic properties of (M = Li, Na, K and Rb) and oxides involving ions and distorted perovskite are discussed in the light of these theoretical results.