Structural and magnetic characterization of BiFexMn2–xO5 oxides (x=0.5, 1.0)

The title compounds have been synthesized by a citrate technique followed by thermal treatments in air (BiFe0.5Mn1.5O5) or under high oxygen pressure conditions (BiFeMnO5), and characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetization measurements. The crystal structures have been refined from NPD data in the space group Pbam at 295 K. These phases are isostructural with RMn2O5 oxides (R=rare earths) and contain infinite chains of Mn4+O6 octahedra sharing edges, linked together by (Fe,Mn)3+O5 pyramids and BiO8 units. These units are strongly distorted with respect to those observed in other RFeMnO5 compounds, due to the presence of the electronic lone pair on Bi3+. It is noteworthy the certain level of antisite disorder exhibited in both samples, where the octahedral positions are partially occupied by Fe cations, and vice versa. BiFexMn2−xO5 (x=0.5, 1.0) are short-range magnetically ordered below 20 K for x=0.5 and at 40 K for x=1.0. The main magnetic interactions seem to be antiferromagnetic (AFM); however, the presence of a small hysteresis in the magnetization cycles indicates the presence of some weak ferromagnetic (FM) interactions.

Graphical AbstractBiFexMn2–xO5 (x=0.5, 1.0) samples are isostructural with BiMn2O5, belonging to the Pbam space group. The crystal structure contains infinite chains of edge-sharing Mn4+O6 octahedra, interconnected by dimer units of Fe3+O5 square pyramids. These units are strongly distorted due to the presence of the electronic lone pair on Bi3+. They are magnetically ordered at low temperatures. The main magnetic interactions seem to be antiferromagnetic with the presence of some weak ferromagnetic response.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Two new compounds of formula BiFexMn2–xO5 (x=0.5, 1.0) have been obtained. ► Their crystallographic structure is isotypical with that of RMn2O5 materials. ► The presence of the electronic lone pair on Bi3+ severely distorts the crystal structure. ► There is no establishment of a long-range ferrimagnetic structure.