Orbital occupation and magnetism of tetrahedrally coordinated iron in CaBaFe4O7

CaBaFe4O7 is a mixed-valent transition metal oxide having both Fe2+ and Fe3+\nions in tetrahedral coordination. Here we characterize its magnetic properties\nby magnetization measurements and investigate its local electronic structure\nusing soft x-ray absorption spectroscopy at the Fe L2,3 edges, in combination\nwith multiplet cluster and spin-resolved band structure calculations. We found\nthat the Fe2+ ion in the unusual tetrahedral coordination is Jahn-Teller active\nwith the high-spin e^2 (up) t2^3 (up) e^1 (down) configuration having a\nx^2-y^2-like electron for the minority spin. We deduce that there is an\nappreciable orbital moment of about L_z=0.36 caused by multiplet interactions,\nthereby explaining the observed magnetic anisotropy. CaBaFe4O7, a member of the\n'114' oxide family, offers new opportunities to explore charge, orbital and\nspin physics in transition metal oxides.\n