Temperature excitation of the Co3+ triplet spin-state in LaCoO3 determined by polarized neutron diffraction

TL;DR

This study investigates the temperature-dependent spin-state transition of Co3+ ions in LaCoO3 using polarized neutron diffraction, revealing a transition from a singlet to a triplet state near 100 K.

Contribution

It provides direct experimental evidence of the spin-state transition in LaCoO3 and quantifies the magnetic moments and covalent spin density at different temperatures.

Findings

Transition from singlet to triplet state near 100 K

High-spin state energy too high to be significant at measured temperatures

Presence of covalent spin density on oxygen ligands

Abstract

The magnetic moment induced by an external magnetic field of 5.8 T on the Co3+ ions in LaCoO3 has been measured by polarized neutron diffraction. Measurements were made at 100 K, near to the spin-state transition, at 1.5 K and at 285 K. The data give evidence for a transition from the ground singlet state (S = 0) to the excited triplet intermediate spin state (S = 1). The energy of K estimated for the high-spin (S = 2) state, is too high to contribute significantly even at T = 285 K. There is evidence for a small negative covalent spin density associated with the oxygen ligands amounting to about one fifth of the aligned Co3+ moment at all three temperatures.