Mössbauer Study of FerrimagneticFe7Se8

Mössbauer spectra of ferrimagnetic ${\mathrm{Fe}}_7$ ${\mathrm{Se}}_8$ have been taken at various temperatures ranging from liquid-nitrogen temperature to the specimen's Néel point. Three sets of six-line hyperfine patterns were obtained and assigned to three magnetically nonequivalent sites of a superstructure of the crystal. Isomer shifts indicate nearly ${\mathrm{Fe}}^{2+}$ for all three sites. Change of sign of quadrupole splittings above and below 130 °K were observed and may be interpreted to be due to the spin-rotation from $c$ axis to $c$ plane with increasing temperature. The Néel temperature was determined to be (447 ± 1) °K.