Crystal/chemical structures and magnetic properties of naturally occurring Mn1.7Fe1.3O4

Abstract

An unusually pure Mnx Fe3−x O4 sample (x≂1.3) from a regionally metamorphosed ore body is expected to exhibit an approach to thermodynamic equilibrium unattainable in synthetic materials. This expectation is confirmed by the observation of (1) a small tetragonal distortion and (2) a complete ordering of Fe on the B sublattice. 57Fe Mössbauer spectra, obtained at 298, 175, 125, and 92 K and in an external field of 30 kG at 92 K, exhibit magnetic hyperfine splitting requiring the fitting of two subspectra, I and II. At 298 K, Heff =418 kOe, α=0.36 mm s−1 , and ε≊0 for the more intense subspectrum I, whereas for II Heff =403 kOe, δ=0.34 mm s−1 , and ε≂−0.15 mm s−1 . The two subspectra are not split by a 30 kG external field. Subspectra I and II correspond to Fe3+ ions located on a single magnetic sublattice. Subspectrum II is assigned to Fe3+ ions in regions with locally, large tetragonal distortions as a consequence of Mn3+clustering, which has often been invoked to explain the crystal chemistry and physical properties of Mnx Fe3−x O4 .

57Fe Mössbauer investigations of manganese-containing spinels

“…Occasions to study manganese-containing spinels that have high degrees of thermal equilibration are rare opportunities to gain insights into order-disorder phenomena and crystal/chemical structures that are of fundamental importance in magnetic and electronic materials [1]. In this report, we present the results of our investigations of just such a suite of Mn-containing spinels.…”

“…In this report, we present the results of our investigations of just such a suite of Mn-containing spinels. The minerals studied in this investigation are iwakiite (Gozaisho mine, Japan [1]), galaxite (Bald Knob, North Carolina [2], and Nakhon Pathom, Thailand), and franklinite (L~mgban, Sweden). Iwakiite samples from the Gozaisho mine are noteworthy inasmuch as manganese ferrites from this locality exhibit unusually high degrees of thermal equilibration and tetragonal distortions at Mn contents well below those observed for synthetic samples.…”