Influence of rare-earth ion radii on the low-spin to intermediate-spin state transition in lanthanide cobaltite perovskites: LaCoO3versusHoCoO3

Abstract

We present first-principles (local-density approximation) LDA+U calculations of electronic structure and magnetic state for ${\mathrm{LaCoO}}_3$ and ${\mathrm{HoCoO}}_3.$ Low-spin to intermediate-spin state transition was found in our calculations using experimental crystallographic data for both materials with a much higher transition temperature for ${\mathrm{HoCoO}}_3,$ which agrees well with the experimental estimations. Low-spin state $t_{2g}^6{e}_g^0$ (nonmagnetic) to intermediate-spin state $t_{2g}^5{e}_g^1$ (magnetic) transition of ${\mathrm{Co}}^{3+}$ ions happens due to the competition between crystal-field $t_{2g}-{\mathrm{e}}_g$ splitting and effective exchange interaction between $3d$ spin orbitals. We show that the difference in crystal structure parameters for ${\mathrm{HoCoO}}_3$ and ${\mathrm{LaCoO}}_3$ due to the smaller ionic radius of Ho ion comparing with La ion results in stronger crystal-field splitting for ${\mathrm{HoCoO}}_3$ $(0.09\mathrm{}\mathrm{eV}\approx 1000\mathrm{K}$ larger than for ${\mathrm{LaCoO}}_3)$ and hence tips the balance between the low-spin and intermediate-spin states to the nonmagnetic solution in ${\mathrm{HoCoO}}_3.$