Interplay of electron correlations, spin-orbit couplings, and structural effects for Cu centers in the quasi-two-dimensional magnet In Cu2/3 V 1/3 O3

Less common ligand coordination of transition-metal centers is often associated with peculiar valence-shell electron configurations and outstanding physical properties. One example is the Fe+ ion with linear coordination, actively investigated in the research area of single-molecule magnetism. Here we address the nature of 3d9 states for Cu2+ ions sitting in the center of trigonal bipyramidal ligand cages in the quasi-two-dimensional honeycomb compound In Cu2/3 V1/3 O3, whose unusual magnetic properties were intensively studied in the recent past. In particular, we discuss the interplay of structural effects, electron correlations, and spin-orbit couplings in this material. A relevant computational finding is a different sequence of the Cu ( xz, yz ) and ( xy, x2 − y2 ) levels compared to existing electronic-structure models, which has implications for the interpretation of various excitation spectra. Spin-orbit interactions, both first- and second-order, turn out to be stronger than previously assumed, suggesting that rather rich single-ion magnetic properties can in principle be achieved also for the 3d9 configuration by properly adjusting the sequence of crystal-field states for such less usual ligand coordination.