Complex Cation and Spin Orders in the High-Pressure Ferrite CoFe3O5.

A ferrite in the Sr2Tl2O5-type MFe3O5 family with M = Co has been synthesized at 12 GPa pressure. Neutron diffraction shows the sample to be Co deficient with composition Co0.6Fe3.4O5. The Co/Fe cation distribution is found to be profoundly different from those of MFe3O5 analogs and lies between normal and inverse limits, as Co2+ substitutes across trigonal prismatic and one of the two octahedral sites. CoFe3O5 shows complex magnetic behavior with weak ferromagnetism below TC1 ≈ 300 K and a second transition to ferrimagnetic order at TC2 ≈100 K. Spin scattering of carriers leads a substantial increase in the hopping activation energy below TC1, and a small negative magnetoresistance is observed at low temperatures.

Long range electronic phase separation in CaFe3O5.

Incomplete transformations from ferromagnetic to charge ordered states in manganite perovskites lead to phase-separated microstructures showing colossal magnetoresistances. However, it is unclear whether electronic matter can show spontaneous separation into multiple phases distinct from the high temperature state. Here we show that paramagnetic CaFe3O5 undergoes separation into two phases with different electronic and spin orders below their joint magnetic transition at 302 K. One phase is charge, orbital and trimeron ordered similar to the ground state of magnetite, Fe3O4, while the other has Fe2+/Fe3+charge averaging. Lattice symmetry is unchanged but differing strains from the electronic orders probably drive the phase separation. Complex low symmetry materials like CaFe3O5 where charge can be redistributed between distinct cation sites offer possibilities for the generation and control of electronic phase separated nanostructures.

Author Correction: Long range electronic phase separation in CaFe3O5.

The original version of this Article contained an error in the third sentence of the legend of Fig. 2, which incorrectly read 'The phase fractions of the charge ordered (CO) phase, obtained from synchrotron (X) and neutron (N) diffraction data are shown in the right-hand panel.' The correct version states 'charge averaged (CA)' in place of 'charge ordered (CO)'. This has been corrected in both the PDF and HTML versions of the Article.