Ferromagnetism and crystal lattice stability of bcc and fcc iron

Nuclear quadrupole coupling constants have previously been determined for a large number of iron-containing compounds by using the Mössbauer effect. In general, the sign of the coupling constant has not been determined although this parameter can have interesting structural implications. We have used the magnetic perturbation technique to determine the sign of the nuclear quadrupole coupling constants in FeSO4, FeSO4·7H2O, FeCO3, FeCl2·4H2O, and FeSiF6·6H2O. A recent proposal that a correlation exists between the isomer shift and quadrupole coupling in ionic ferrous compounds and that this correlation can be used to infer the sign of the latter is found to be incorrect.

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The existence of magnetic transitions in alloys of Fe in Au and Cu has been shown by using the Mössbauer effect. There is a significant difference in the internal-field distribution (and hence alignment of the atomic spins) between the Cu and the Au alloys. In the former a continuous distribution exists, whereas, in the latter a unique (or very nearly unique) internal field occurs in the dilute alloys. The results for the Cu alloys are consistent with an indirect interaction of the Ruderman-Kittel-Yosida type of spins localized at the iron atoms. The internal-field distribution appears to develop a minimum at zero field and a rather broad maximum which shifts gradually to higher fields with decreasing temperature. The nearly unique internal field in the dilute Au-Fe alloys seems to exclude an explanation on the basis of a Ruderman-Kittel-Yosida exchange interaction. A spiral static spin density wave as the mechanism for antiferromagnetically ordering the localized spins (or ferromagnetic order for the case in which the spin density wave vector is zero) seems possible. More concentrated Au-Fe (>16 at. % Fe) alloys show a much more rapid increase in the magnetic transition temperature than the more dilute alloys. Their behavior is ferromagnetic and can be described quite well with a nearest-neighbor interaction using the average coordination number method suggested by Sato, Arrott, and Kikuchi. The appropriate nearest-neighbor exchange interaction energy is J≃2.9×10−2 eV.

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Summary.Oxides of the Cu-Fe-O system prepared by solid-state reaction methods have been investigated by X-ray, MSssbauer effect, and analytical chemical techniques. In agreement with most previous investigations of this system, it is found that CuFcO~ exists as a stable compound, and that the mineral delafossite has essentially this composition. These results are in disagreement with those of Buist, Gadalla, and White who propose that delafossite has an approximate composition Cu~FeaO ~ instead of CuFeO~. In fact, a compound of composition Cu~F%O7 could not be prepared. The MSssbauer isomer shift provides confirmation that the iron in CuFeO~ is trivalent. CONTRARY to previous findings, e Buist, Gadalla, and White (1966) (see also Gadalla and White, 1966) came to the conclusion that the compound CuFeO~, commonly considered to be the same as the mineral delafossite, does not exist. Instead, they postulated the existence of a new compound of the approximate composition Cu6FeaO 7 (~ 3Cu20.F%O4). The latter composition was derived from the measured weight loss during heating on a thermobalance and the initial composition of mixtures of CuO and F%0 a. No chemical analysis of the resulting compound was given. From X-ray powder diffraction patterns Bnist et al. (1966) (Muir and Wiedersich, 1967) have studied CuFeO 2 and the mineral delafossite using the MSssbauer effect (ME) without 1 Present address:

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Lunar bulk sample 10084,85 (< 1 mm size dust), and samples from rocks 10017,17 (fine grained, vesicular), 10046,17 (breccia), 10057,59 (fine grained, vesicular, top surface), 10057,60 (fine grained, vesicular, interior), and 10058,24 (medium grained, not vesicular) have been investigated by (57)Fe Mössbauer spectroscopy. Iron metal and the Fe(2+) minerals ilmenite, pyroxene, troilite, and iron containing glass have been identified. An iron line of sample 10084,85 (originally sealed in nitrogen) showed no significant intensity change when the sample was exposed to air. The antiferromagnetic transition in several lunar ilmenites at 57(0) +/- 2 degrees K corresponds to stoichiometric FeTiO,. Magneticallv separated 10057 showed troilite and somne metallic iron.