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 .