$\mathrm{CaFe}{\mathrm{O}}_3$ and $\mathrm{CaF}{\mathrm{e}}_{0.95}\mathrm{C}{\mathrm{o}}_{0.05}{\mathrm{O}}_3$ single crystals were grown by combing floating-zone method with high oxygen pressure treatment. Both crystals show charge disproportionation of Fe ($\mathrm{F}{\mathrm{e}}^{4+}\to \mathrm{F}{\mathrm{e}}^{3+}+\mathrm{F}{\mathrm{e}}^{5+}$) accompanied by a metal-to-insulator transition as well as a crystal structural transformation from Pbnm to $P{2}_1/n$. However, the slight introduction of Co significantly suppresses the critical temperature of charge disproportionation from 290 K in $\mathrm{CaFe}{\mathrm{O}}_3$ to 260 K in $\mathrm{CaF}{\mathrm{e}}_{0.95}\mathrm{C}{\mathrm{o}}_{0.05}{\mathrm{O}}_3$. Different from the single antiferromagnetic phase transition as observed in the polycrystalline $\mathrm{CaFe}{\mathrm{O}}_3$, two sequential antiferromagnetic transitions are found to occur in these two single crystals with the Néel temperatures around 119 and 112 K for $\mathrm{CaFe}{\mathrm{O}}_3$ crystal and 109 and 98 K for $\mathrm{CaF}{\mathrm{e}}_{0.95}\mathrm{C}{\mathrm{o}}_{0.05}{\mathrm{O}}_3$ crystal, respectively. Neutron diffraction illustrates the formation of a spiral antiferromagnetic structure. Moreover, as the temperature further decreases to 65 K, a third magnetic transition accompanied by a second electrical transition is observed in the slightly Co-doped $\mathrm{CaF}{\mathrm{e}}_{0.95}\mathrm{C}{\mathrm{o}}_{0.05}{\mathrm{O}}_3$ crystal. First-principles calculations suggest that the introduction of a moderate amount of Co and the peculiar spiral spin texture play an important role in the presence of such new magnetic and electrical transitions.

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• Charge order
• High-pressure studies
• Magnetism
• Metal-insulator transition
• Perovskites
• Single crystal materials
• Transition metal oxides
• Density functional calculations
• Mössbauer spectroscopy
• Neutron diffraction