Influence of Co$^{3+}$ spin-state on optical properties of LaCoO$_3$ and HoCoO$_3$

TL;DR

This study investigates how the spin state of Co$^{3+}$ ions influences the optical properties of LaCoO$_3$ and HoCoO$_3$, revealing spectral shifts and intensity changes linked to spin-state differences through experimental and theoretical analysis.

Contribution

It provides new insights into the relationship between Co$^{3+}$ spin states and optical spectra in these compounds using combined experimental measurements and LDA+U calculations.

Findings

Spectral features shift to higher energies in HoCoO$_3$ due to lattice distortions.

Absorption intensity increases in HoCoO$_3$ in the 1.3-2.3 eV range.

Onset of absorption shifts from <0.1 eV in LaCoO$_3$ to 0.7 eV in HoCoO$_3$.

Abstract

Optical properties of the isoelectronic compounds LaCoO$_3$ and HoCoO$_3$ has been experimentally and theoretically investigated. We've measured the real $\epsilon_1(\omega)$ and imaginary $\epsilon_2(\omega)$ parts of the dielectric function, reflectance $R(\omega)$ and optical conductivity at room temperature. The shift of the most pronounced spectral features to the high energy region on 0.3 eV associated with larger distortions due to the smaller rare earth ionic radii in HoCoO$_3$ in comparison with LaCoO$_3$ was observed. Also there was found an enhancement of absorption intensity in the range 1.3-2.3 eV in all kinds of spectra in HoCoO$_3$, which can be attributed basing on the results of LDA+U calculations to the different spin-states of Co$^{3+}$ ion in these compounds. The shift of the onset of the absorption from less than 0.1 eV in LaCoO$_3$ to 0.7 eV in HoCoO$_3$ and an absorption intensity enhancement in a narrow spectral range 1.2-2.6 eV in HoCoO$_3$ are clearly seen from the calculated convolution of partial densities of states obtained in the LDA+U approach. Such changes are assumed to be induced by the different Co$^{3+}$ spin-state in these compounds at room temperature.