Influence of rare-earth ion radii on the low-spin to intermediate-spin state transition in lanthanide cobaltite perovskites: LaCoO3 versus HoCoO3

We present first-principles (local-density approximation) LDA+U calculations of electronic structure and magnetic state for LaCoO3 and HoCoO3. 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 HoCoO3, 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 Co3+ ions happens due to the competition between crystal-field t(2g)-e(g) splitting and effective exchange interaction between 3d spin orbitals. We show that the difference in crystal structure parameters for HoCoO3 and LaCoO3 due to the smaller ionic radius of Ho ion comparing with La ion results in stronger crystal-field splitting for HoCoO3 (0.09 eVapproximate to1000 K larger than for LaCoO3) and hence tips the balance between the low-spin and intermediate-spin states to the nonmagnetic solution in HoCoO3.