Exchange interactions between V2+ions in magnesium oxide

The exchange interaction between pairs of V 2+ ions occupying substitutional cation sites in magnesium oxide has been studied by electron paramagnetic resonance. For next nearest neighbour pairs coupled via an intervening oxygen ion, transitions within the total spin state S=2 only are observed. Transitions within the S=1 and S=3 levels are broadened by interactions which leave the S=2 level unaffected. The exchange-induced fine structure splitting, D e , is almost a factor of two larger than the dipolar term D d . Although lattice distortion, covalent spin transfer to the ligands and anisotropic exchange interactions may contribute to this discrepancy a significant part must come from so far undetermined mechanisms. The nearest neighbour pairs, which are at right angles with respect to an intervening anion, have been studied in less detail. The interaction is found to be ferromagnetic with J=-7.5+or-3 cm -1 .