We studied the spin-state responses to light impurity doping in low-spin perovskite LaCoO$_{3}$ (Co^3+: d^6) through magnetization and X-ray fluorescence measurements of single-crystal LaCo$_{0.99}$$M_{0.01}$O$_{3}$ ($M$ = Cr, Mn, Fe, Ni). In the mag
netization curves measured at 1.8 K, a change in the spin-state was not observed for Cr, Mn, or Fe doping but was observed for Ni doping. Strong magnetic anisotropy along the [100] easy axis was also found in the Ni-doped sample. The fluorescence measurements revealed that the valences were roughly estimated to be Cr^3+, Mn^4+, Fe^(3+delta)+, 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, we discuss the emergence of highly anisotropic ferromagnetic spin-state clusters induced by low-spin Ni^3+ with Jahn-Teller activity. We also discuss applicability of the present results to mantle materials and impurity-doped pyrites with Fe (d^6).
