Cation, magnetic, and charge ordering in MnFe3O5

Abstract

The recently-discovered high pressure material MnFe₃O₅ displays a rich variety of magnetically ordered states on cooling. Fe spins order antiferromagnetically below a Néel transition at 350 K. A second transition at 150 K marks Mn spin order that leads to spin canting of some of the Fe spins and ferrimagnetism. A further transition at 60 K is driven by charge ordering of Fe²⁺ and Fe³⁺ over two inequivalent Fe sites, with further canting of all spins. Electrical resistivity measurements reveal semiconducting behaviour in MnFe₃O₅ with a change in activation energy at 285 K.

Fig. 1. (left) Zero-field cooled and field cooled magnetisation measurements between 2 and 400 K. (right) Magnetisation-field hysteresis loops for MnFe₃O₅ measured at 2, 75, 300 and 400 K.

Fig. 2. Temperature evolution of the neutron diffraction pattern of MnFe₃O₅. Magnetic contributions appear at 300 K, and arrows indicate additional magnetic peaks at 5 K, with hkl = (001) and (003) at d-spacing = 12.6 and 4.2 Å, respectively.

Fig. 3. Rietveld refinement of high resolution neutron diffraction patterns of MnFe₃O₅ obtained at 5 K, with upper tick marks indicating nuclear peaks and lower presenting magnetic reflections. (R_wp = 12.9% and R_p = 12.6%).

Fig. 4. (a) Magnetic structures of MnFe₃O₅ at 5, 75 and 300 K. The network of FeO₆ octahedra is shown, with Mn²⁺ in trigonal prismatic sites within channels parallel to the a-axis. (b) The temperature evolution of the ordered Mn, Fe1 and Fe2 magnetic moments. (c) Temperature evolution of BVS and Q_JT, with closed/open symbols representing Fe1/Fe2 sites.

Fig. 5. Changes in the lattice parameters and cell volume obtained from powder synchrotron X-ray diffraction experiments.

Fig. 6. Log of electrical resistivity of MnFe₃O₅ measured between 260 and 380 K, with insert showing the plot against reciprocal temperature.