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

We studied the spin-state responses to light impurity substitution in low-spin perovskite LaCoO₃ (Co3⁺: d6) through magnetization, x-ray fluorescence, and electrical resistivity measurements of single-crystal LaCo_0.99M_0.01O₃ (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 Cr3⁺, Mn⁽4^-δ ⁾⁺, Fe⁽3⁺δ ^′)+, and Ni3⁺. 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, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.101.247603 101, 247603 (2008)], the emergence of highly anisotropic spin-state molecular ferromagnets induced by low-spin Ni3⁺ with Jahn-Teller activity is suggested. We also discuss applicability of the present results to other materials with Fe (d6).