A Study of the Low Temperature Transition in Magnetite

Abstract

A study of the low temperature transition in magnetite has been performed by the Mössbauer absorption using both an isotopic enriched sample and a single crystal. At room temperature two different hyperfine fields 495±20 kOe and 470±20 kOe were observed, and their intensity ratio was about one to two. Below the transition temperature, hyperfine fields of 510±20 kOe and 470 -20 +30 kOe were observed and their intensity ratio was about two to one providing the ferric and ferrous ions in octahedral sites to be separately ordered. An electric quadrupole interaction and an isomer shift for the ferrous ions were carefully measured as -1.9±0.2 mm/sec and 0.88±0.15 mm/sec, respectively, at 85°K. These values are a little smaller than those in the ordinary ferrous compounds. A weak peak was observed, which could not be identified. A temperature dependence of the absorption spectra was also observed in the transition region. It is suggested that two phenomena described in the paper are superposed in this temperature region.