Spin-Reorientation and Mossbauer Study of Orthoferrite TbFe0.75Mn0.25O3

The crystallographic and magnetic properties of TbFe0.75Mn0.25O3 powder were characterized by x-ray diffraction (XRD), Mossbauer spectroscopy, and vibrating-sample magnetometry (VSM). The crystal structure was found to be orthorhombic (space group Pbnm) with lattice constants a (0)=5.317 , b (0)=5.604 , and c (0)=7.598 , respectively. Mossbauer spectra of TbFe0.75Mn0.25O3 have been taken at various temperatures ranging from 4.2 to 550 K. For Mossbauer spectra, we have fitted the spectra to a model based on a random distribution of Fe and Mn ions on the octahedral sites. The magnetic hyperfine fields of the four pattern (B (0),B (1),B (2),B (3)) at 4.2 K are found to be H (hf)=553, 544, 535, and 527 kOe, respectively. Isomer shift at room temperature is 0.25-0.26 mm/s, which means that the valence state of Fe ions is ferric (Fe3+). A sudden change in both the magnitude of magnetic hyperfine field and its slope between 150 and 220 K suggests that magnetic phase transition related to the spin ordering takes place abruptly. The N,el temperature was determined to be T (N)=550 +/- 5 K. The inflection points arising from a spin reorientation in the temperature dependence of the magnetic moment is observed. Its spin-reorientation transition is 70 K lower than that of 250 K for pure TbFeO3.