Proximate electronic and magnetic phase transitions in CaFe3O5

Electronic phase separation in lightly-doped CaFe3O5 has been investigated through a variable temperature powder neutron diffraction study of CaFe2.99M0.01O5 (M = Co, Mn) samples. This reveals a complex series of proximate phase transitions. Lattice strains resulting from the onset of charge order (CO) drive formation of a competing charge averaged (CA) phase that emerges at TCA = TCO = 320 K. The CA phase emerges as magnetically ordered but the long range spin ordering transition is limited by domain growth and so occurs at a slightly lower temperature (TCA(m) = 301 K for both samples). Magnetic ordering in the CO phase is not directly coupled to the other transitions, but is nearby in temperature with TCO(m) = 290(1) and 292(1) K for M = Co and Mn samples. The remarkable coincidence of energy scales for the formation of two distinct electronic ground states with differing lattice strains and their long range spin orders thus results in electronic and magnetic phase separation through a series of thermally proximate phase transitions in lightly-doped CaFe3O5.