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

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.