Temperature dependence of the spin state of a Co$^{3+}$ Ion in RCoO$_3$ ($R$ = La, Gd) cobaltites

Changes in the spin state of Co$^{3+}$ ions in LaCoO$_3$ and GdCoO$_3$ compounds are studied through the use of the temperature dependence of the magnetic susceptibility and the modified crystal field theory. It is shown that the spin subsystem of Co$^{3+}$ ions in LaCoO$_3$ and GdCoO$_3$ undergoes the spin-crossover type transition between the high-spin ($S = 2$) and low-spin ($S = 0$) states without any contribution of the intermediate-spin state ($S = 1$).