Strongly-correlated crystal-field approach to 3d oxides - the orbital   magnetism in 3d-ion compounds
  We have developed the crystal-field approach with strong electron correlations, extended to the Quantum Atomistic Solid-State theory (QUASST), as a physically relevant theoretical model for the description of electronic and magnetic properties of 3d-atom compounds. Its applicability has been illustrated for LaCoO3, FeBr2 and Na2V3O7. According to the QUASST theory in compounds containing open 3d-/4f-/5f-shell atoms the discrete atomic-like low-energy electronic structure survives also when the 3d atom becomes the full part of a solid matter. This low-energy atomic-like electronic structure, being determined by local crystal-field interactions and the intra-atomic spin-orbit coupling, predominantly determines electronic and magnetic properties of the whole compound.   We understand our theoretical research as a continuation of the Van Vleck's studies on the localized magnetism. We point out, however, the importance of the orbital magnetism and the intra-atomic spin-orbit coupling for the physically adequate description of real 3d-ion compounds and 3d magnetism. Our studies clearly indicate that it is the highest time to ''unquench'' the orbital moment in solid-state physics in description of 3d-atom containing compounds.   PACS No: 75.10.D; 71.70.E   Keywords: magnetism, transition-metal compounds, 3d magnetism, crystal field, spin-orbit coupling, orbital magnetism 
R.J. Radwanski and Z. Ropka