Electronic and spin configurations of Co³⁺ and Ni³⁺ ions in oxides of K₂NiF₄ structure: a magnetic susceptibility study

Abstract

In La₄LiCoO₈, Li⁺ and Co³⁺ ions are ordered in two dimensions and Co³⁺ ions undergo transitions from the low-spin to the intermediate as well as the high-spin states. Both Sr₄TaCoO₈ and Sr₄NbCoO₈ exhibit low to intermediate-spin state transitions of Co³⁺ ions. In the system LaSr_1−xBa_xNiO₄, the e_g electrons are essentially in extended states forming a σ^∗_x²−y² band. With increase in x, the band width decreases accompanying an increase in unit cell volume; high-spin Ni³⁺ ions are formed to a small extent with increasing x, but there is no spin-state transition. In LaSrAl_1−xNi_xO₄, at small x, there is a small proportion of high-spin Ni³⁺; when x≈0.6, there is an abrupt decrease in the c̲/a̲ ratio, signalling the formation of the σ^∗_x²−y² band. In LnSrNiO₄, the c̲/a̲ ratio decreases sharply between Ln=La and Nd; this is likely to be accompanied by a broadening of the σ^∗_x²−y² band.