Valence and spin states in perovskites LaCo0.95M0.05O3 (M = Mg, Ga, Ti)

TL;DR

This study investigates how dilute heterovalent doping in LaCoO3 perovskites affects their magnetic and transport properties up to 900 K, revealing stable magnetic polarons and doping-specific behaviors.

Contribution

It provides new insights into the effects of heterovalent dopants on valence and spin states in LaCoO3, highlighting differences from non-stoichiometric and La-site doped variants.

Findings

Doping does not alter the magnetic transition at ~100 K.

Hole carrier onset occurs at ~500 K regardless of doping.

Doped samples with extra charge form thermally stable magnetic polarons.

Abstract

The samples LaCoO3 with dilute substitutions on cobalt sites have been studied using the resistivity, thermopower and magnetic susceptibility measurements over the temperature range up to ~900 K. The Co-site substitution does not affect the magnetic transition at ~100 K and the onset of massive population of hole carriers at ~500 K, characteristic for undoped LaCoO3. On the other hand, the low-temperature transport and magnetism is markedly distinct for samples with extra charge on cobalt ions introduced by the heterovalent dopants (Mg2+, Ti4+) compared to samples with minor non-stoichiometry (LaCoO3, Ga3+ doped sample). Magnetic properties suggest that these extra charges create thermally stable magnetic polarons of total S ~ 2-3. Common features of Co-site doped and La-site doped samples (La1-xSrxCoO3) are discussed