Magnetic properties of the iron selenide Fe7Se8

The magnetic properties of the “3c” and “4c” phases of the iron selenide, Fe7Se8, have been studied. Mössbauer spectra have been analyzed in terms of overlapping six-line patterns and identified with iron ions in the different crystallographic sites, called A, B, and C. The isomer shifts indicate that all the cations are in the ferrous state. The hyperfine fields, quadrupole shifts, and magnetization measurements for the 3c structure provide evidence for the abrupt change in the spin direction at about T = 130 K. Cold working the samples, even for a brief period of time, led to the appearance of large absorption in the central region of the Mössbauer spectra; it is suggested that new phases had been introduced.