A Mössbauer study of , having the olivine structure: comparison with fayalite and related minerals

Abstract

has the olivine structure Pnma with , and at room temperature. The Mössbauer spectrum at 295 K consists of two doublets having centroid shifts (relative to ) and quadrupole splittings for the two metal positions Fe1 (point symmetry ) and Fe2 (point symmetry m) of , and . A point charge calculation for the nearest S octahedra gives the Mössbauer asymmetry parameters and for Fe1 and Fe2 respectively, and for both positions. At approximately 130 K there is an antiferromagnetic transition, and a second transition to a ferromagnetic or ferrimagnetic structure takes place at approximately 30 K. Both magnetic regions show complicated Mössbauer spectra, which require the full Hamiltonian for their analysis. Comparisons are made with Mössbauer results on the related minerals (fayalite), (iron sarcopside), and .

Magnetisation and Mössbauer studies of (Fe1-xMex)2SiS4,x≤ 0.25 andMe= Co or Ni

“…Furthermore, it was shown that the difference in centroid shift value for the two sites was CS(M2) ^CS(M1) % 0.04 mm/s for all samples at room temperature. The same result can be derived from earlier studies of Fe 2 SiS 4 in the AFM region [7]. The same difference in CS-values is also found in the AFM region for the 5% Co and 5% Ni samples.…”

“…Substitution with Co and Ni increases T N : A detailed study of the Mossbauer absorption pro¢les gave T N 126 K for Fe 2 SiS 4 , 132 K for (Fe 0.75 Co 0.25 ) 2 SiS 4 and 155 K for (Fe 0.75 Ni 0.25 ) 2 SiS 4 . Avery big difference in hyper¢ne ¢elds for iron at M1 and M2 in the AFM phase, as already found for Fe 2 SiS 4 [7] is also seen here for all samples, e.g. at T % 10 K, (Fe 0.75 Ni 0.25 ) 2 SiS 4 has B(Ml) % 30 tesla and B(M2) % 6 tesla.…”

“…The ¢tting model and a con¢rmed assignment.We have earlier published MS results on Fe 2 SiS 4 [7]. It was shown that the MS signals from iron at M1 and M2 were of closely equal strength and did not vary with temperature, thus the two positions have nearly equal f-factors.…”

“…Thus, the old assignment used in refs. [7] and [9] is correct and the proposed new assignment used in ref. [4] is wrong.…”

Predicted thermoelectric properties of olivine-type Fe2GeCh4(Ch = S, Se and Te)

“…The arrangement of the atoms in the crystal is very closely packed and resembles hexagonal close packed arrangement. Among the olivine structures, F e based olivines are well known because of their diverse magnetic nature at low and high temperatures [2,3,4]. In the case of Fe 2 GeS 4 , it was found to possess weak ferromagnetic nature upto 69 K, anti-ferromagnetic nature between 69-143 K and above this temperature it is reported to be in paramagnetic nature [5].…”