Spin-state responses to light impurity substitution in low-spin perovskite LaCoO3

Abstract

We studied the spin-state responses to light impurity substitution in low-spin perovskite LaCoO${}_{3}$ (Co${}^{3+}$: ${d}^{6}$) through magnetization, x-ray fluorescence, and electrical resistivity measurements of single-crystal LaCo${}_{0.99}{M}_{0.01}$O${}_{3}$ ($M$ $=$ Cr, Mn, Fe, Ni). In the magnetization curves measured at 1.8 K, a change in the spin-state was not observed for Cr, Mn, or Fe substitution but was observed for Ni substitution. Strong magnetic anisotropy was also found in the Ni-substituted sample. The fluorescence measurements revealed that the valences were roughly estimated to be Cr${}^{3+}$, Mn${}^{(4\ensuremath{-}\ensuremath{\delta})+}$, Fe${}^{(3+{\ensuremath{\delta}}^{\ensuremath{'}})+}$, and Ni${}^{3+}$. From the observed chemical trends, we propose that the chemical potential is a key factor in inducing the change of the low-spin state. By expanding a model of the ferromagnetic spin-state heptamer generated by hole doping [Podlesnyak et al., Phys. Rev. Lett. 101, 247603 (2008)], the emergence of highly anisotropic spin-state molecular ferromagnets induced by low-spin Ni${}^{3+}$ with Jahn-Teller activity is suggested. We also discuss applicability of the present results to other materials with Fe (${d}^{6}$).