The spin states of Co ions in La1.5Ca0.5CoO4 from first-principles

TL;DR

This study uses first-principles calculations to determine the spin states and electronic structure of La1.5Ca0.5CoO4, revealing stable low-spin Co3+ and high-spin Co2+ states, and clarifying magnetic properties and spin-state stability.

Contribution

It provides a detailed first-principles analysis of the spin states in La1.5Ca0.5CoO4, challenging previous experimental suggestions of mixed states and clarifying the electronic and magnetic structure.

Findings

Co2+ is in a high-spin state

Co3+ is in a low-spin state

The results explain magnetic anisotropy and low magnetic ordering temperature.

Abstract

The spin states and electronic structure of layered perovskite La1.5Ca0.5CoO4 are investigated using fullpotential linearized augmented plane-wave method. All the computational results indicate that the Co2+ ion is in a high-spin state and the Co3+ in a low-spin state. The Co2+ t2g orbitals with a small crystal-field splitting are mixed by spin-orbit coupling, which accounts for the observed easy in-plane magnetism. The nonmagnetic LS-Co3+ state, which is stabilized by a strong crystal field, provides a natural explanation for the observed low magnetic ordering temperature and a spin-blockade phenomenon of the electron hopping. Furthermore, we find that the intermediate-spin state of Co3+ has a large multiplet splitting. But the lowest-lying IS state of Co3+ is still higher in energy than the LS ground state by a few hundred millielectron volts and the HS state of Co3+ is even less stable, both in sharp contrast to a recent experimental study which suggested the HS+IS mixed Co3+ ground state. We note that either the IS-Co3+ or HS-Co3+ states or their mixture would produce a wrong out-of-plane magnetic anisotropy and a much higher magneticordering temperature than observed. Thus, the present work sheds light on this material concerning its electronic and magnetic structure, and it would stimulate different experiments to settle this intriguing spin-state issue.