Magnetic studies of Mn0.2Cr1.8−x Fe x O3 nano oxides prepared via hydrothermal route

Abstract

Manganese–iron chromium oxides (Mn0.2Cr1.8−xFexO3) with x varying from 0.3 to 1.3 have been produced by hydrothermal process in a stirred pressure reactor from pure metal chlorides. Single phase corundum structure and nanophase structure of the as-synthesized samples were confirmed by X-ray diffraction and by transmission electron microscope. The results show that the produced powders have an average size of 23 nm. The Mossbauer spectra recorded at about 300 K show transition from paramagnetic to ordered magnetic spin state. The shift in hysteresis loops observed along the magnetic field axis is associated with exchange bias effect. The exchange bias field increases as the particle size decreases with increased Fe content x. The loop shifts are different with different particle sizes suggesting that the materials at room temperature may be superparamagnetic.