Study of the Low-Temperature Transition in Magnetite and the Internal Fields Acting on Iron Nuclei in Some Spinel Ferrites, Using Mössbauer Absorption

Abstract

A study has been made of the internal fields acting on Fe 57 nuclei in some spinel ferrites, with particular reference to the low-temperature order-disorder transition in magnetite, using the techniques of Mossbauer absorption. For the Fe 3+ ions at both the octahedral and tetrahedral sites in nickel ferrite (NiFe 2 0 4 ) at 300°K, 7Fe20 3 at 85° and 300°K, and magnetite (Fe30 4 ) at 85 °K, the effective magnetic field at the Fe 67 nuclei is the same and equal to about 5.1 XlO 5 oe. In magnetite, the value of H e u in the Fe 2+ ions is about 4.5X10 5 oe at 85°K. Measurements on Fe 3 04 at room temperatures provide a microscopic confirmation of Verwey's hypothesis that above the transition temperature of magnetite there is a fast exchange between the ferrous and ferric ions in the octahedral sites.

Magnetotransport properties depending on the nanostructure of Fe3O4nanowires

“…The determination of stoichiometry using Mössbauer spectroscopy is based on the rapid electron hopping process at room temperature. Since this hopping process is much faster than the lifetime of the excited 57 Fe nucleus, the B site ions appear as one average 'Fe 2.5+ '-like component [12]. Therefore, at room temperature, the Mössbauer spectrum of Fe 3 O 4 will contain only two components: one originating from the A sites containing Fe 3+ ions, and the other from the B sites containing Fe 2.5+ ions.…”

The Influence of Aluminum on Iron Oxides: XIV. Al-Substituted Magnetite Synthesized at Ambient Temperatures

“…Because of electron delocalization on the octahedral sites, the room-temperature M6ssbauer spectrum of magnetite comprises two magnetic sextets, one each for Fe 3+ on the tetrahedral sites and Fe with a nominal average valence of 2.5 on the octahedral sites (Bauminger et al, 1961). For pure, stoichiometric magnetite, the intensity ratio of the tetrahedral to octahedral site resonance is 1:2; the hyperfine fields for these are 49.0 and 46.0 T, and the isomer shifts (relative to metallic Fe) are 0.25 and 0.67 ram/s, respectively.…”

Preparation of Glass-Ceramics Containing Ferrimagnetic Zinc-Iron Ferrite for the Hyperthermal Treatment of Cancer

“…Figures 10(a) and (b) show the Mossbauer spectra at 300 K of the powders heat treated at 1150 C for 1 and 5 h in a 95CO 2 {5H 2 atmosphere, together with the assignment of each peak based on the data reported for glasses containing iron ion 24) and magnetite. 25) The isomer shift and hyperfine field are given in Table 2, as well as the atomic fraction of each iron ion in the different sites, which was estimated from the intensity of the respective spectra. It can be seen from Fig.…”