Synthesis, structure and properties of new layered oxyselenides Nd2(Fe1−xMnx)2Se2O3

A new series of layered oxyselenides Nd2(Fe1−xMnx)2Se2O3 (0 ⩽ x ⩽ 0.5) was synthesized via solid state reaction method. Their structure and properties were investigated by the X-ray powder diffraction, magnetic bulk, electrical and thermal transport measurements along with specific heat experiments. The compounds crystallize in the layered tetragonal structure with I4/mmm space group and show semiconducting behavior. The large discrepancy between activation energy for conductivity, Eρ (0.153-0.177 eV), and thermopower, ES (7.0-14.8 meV), indicates the polaronic transport mechanism. Heat capacity and bulk magnetization indicate an increased ferromagnetic component of the long-range magnetic order and possible increased degree of frustration. Atomic disorder on Fe/Mn sites suppresses the temperature of the long-range order whereas intermediate alloys show a rich magnetic phase diagram.