Magneto-polaron formation and field-induced effects with dilute doping in LaCo_1-y Ni _y O₃

Dilute magnetic ion doping in LaCo_1-y Ni _y O ₃ with y≤1 % leads to the formation of isotropic magnetic clusters that exhibit intracluster interactions which are ferromagnetic in nature. The clusters are comprised of Ni ions surrounded by six magnetically polarized Co ions. The Ni spin is delocalized from the Ni³⁺ ion but is confined in the vicinity of the six Co coordinated environment forming small magneto-polarons. The cluster ground state is estimated from bulk magnetization to be about gS∼10, in contrast to LaCoO₃, which is not magnetic. Using neutron spectroscopy, transitions are observed between the lowest energy levels indicating that the cluster ground state is split. Under a magnetic field of 1 Tesla, the transitions are suppressed while with increasing temperature, the intracluster transitions are overshadowed by the activation of the Co ³⁺ ions to the intermediate spin state.