Study of the nuclear and magnetic structures of Mn-Cr ferrite and their temperature dependences

Abstract

Neutron diffraction experiments on a polycrystalline Manganese Chromium ferrite sample with composition MnosCrosFe204 have been done as a function of temperature in the range 768K 2> T 2> 13K. The experiments were performed using a Position Sensitive Detector (PSD) based powder diffractometer with a monochromatic neutron beam of wavelength 1.09 A at the 100 MW Dhruva reactor of Bhabha Atomic Research Center (BARe), India. The reactor was being operated at 65 MW power level during the experiments. The Mn-Cr mixed ferrite has cubic spinel structure and possesses the symmetry of the space group Fd3m. The chemical structure of the sample in respect of the distribution of cations at different crystal lattice sites, oxygen position parameter and the lattice constants have been determined from the Rietveld refinement of the higher angle data. All Mn+2ions and 0.46 atom/formula unit ofCr+3 have been found to occupy the tetrahedral A site. The lattice constant at 300K is found to be 8.5061 A which increases with the temperature. Sublattices and net ferrimagnetic moments of the specimen at different temperatures have been determined from the analysis of the neutron diffraction data. Nee! collinear type of ordering of the magnetic moment has been .found with slight canting effect in the B sublattice. The magnitude of the magnetic moments of A site and B site are found to be -3.08 IlB and 4.39 IlB respectively at 13K. The transition temperature (TN) of the specimen is found to be 530K. The saturation magnetization is found to be 12.5 emu/gm from the magnetization measurement using Vibrating Sample Magnetometer (VSM) at room temperature.