To investigate the emergent properties that may arise from the interplay of different instabilities in orbitally degenerate systems, we consider the representative case of mixed compounds of ${\mathrm{CaFeO}}_3$ and ${\mathrm{LaMnO}}_3$, having isoelectronic B cations. First-principles study of the mixed systems reveals an intricate interplay of charge transfer, Jahn-Teller distortion, and charge disproportionation, influencing the electronic and magnetic properties of the mixed compounds. Although the ground states of both parent compounds are insulating, one being nearly ferromagnetic (FM; ${\mathrm{CaFeO}}_3$) and another antiferromagnetic (AFM; ${\mathrm{LaFeO}}_3$), several of the mixed compounds among the studied compositions, e.g., ${\mathrm{Ca}}_{0.75}{\mathrm{La}}_{0.25}{\mathrm{Fe}}_{0.75}{\mathrm{Mn}}_{0.25}{\mathrm{O}}_3, {\mathrm{Ca}}_{0.625}{\mathrm{La}}_{0.375}{\mathrm{Fe}}_{0.625}{\mathrm{Mn}}_{0.375}{\mathrm{O}}_3, {\mathrm{Ca}}_{0.375}{\mathrm{La}}_{0.625}{\mathrm{Fe}}_{0.375}{\mathrm{Mn}}_{0.625}{\mathrm{O}}_3$, and ${\mathrm{Ca}}_{0.25}{\mathrm{La}}_{0.75}{\mathrm{Fe}}_{0.25}{\mathrm{Mn}}_{0.75}{\mathrm{O}}_3$, turned out to be FM half-metals. The computed $T_c$ values for ${\mathrm{Ca}}_{0.75}{\mathrm{La}}_{0.25}{\mathrm{Fe}}_{0.75}{\mathrm{Mn}}_{0.25}{\mathrm{O}}_3$ and ${\mathrm{Ca}}_{0.25}{\mathrm{La}}_{0.75}{\mathrm{Fe}}_{0.25}{\mathrm{Mn}}_{0.75}{\mathrm{O}}_3$ are found to be reasonably high, having potential applications for spintronics. The ${\mathrm{Ca}}_{0.5}{\mathrm{La}}_{0.5}{\mathrm{Fe}}_{0.5}{\mathrm{Mn}}_{0.5}{\mathrm{O}}_3$ and ${\mathrm{Ca}}_{0.125}{\mathrm{La}}_{0.875}{\mathrm{Fe}}_{0.125}{\mathrm{Mn}}_{0.875}{\mathrm{O}}_3$ compounds, on the other hand, exhibit insulating, AFM behavior, ${\mathrm{Ca}}_{0.875}{\mathrm{La}}_{0.125}{\mathrm{Fe}}_{0.875}{\mathrm{Mn}}_{0.125}{\mathrm{O}}_3$ being FM and insulating. This results in several electronic and magnetic phase transitions as a function of $x$ in ${\mathrm{Ca}}_x{\mathrm{La}}_{1-x}{\mathrm{Fe}}_x{\mathrm{Mn}}_{1-x}{\mathrm{O}}_3$ mixed compounds. Furthermore, an interesting atomic-scale microstructure appears from the competing nature of metal-oxygen covalency.

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• Electronic structure
• Jahn-Teller effect
• Valence
• Transition metal oxides
• Density functional calculations