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See detailDetermination of the antimony valence state in Eu10Mn6Sb13
Brown, D. E.; Johnson, C. E.; Grandjean, Fernande ULg et al

in Inorganic Chemistry (2004), 43(4), 1229-1234

The antimony-121 Mossbauer spectra of Eu10Mn6Sb13 have been measured between 2 and 295 K. Although the Zintl formalism indicates that the nine crystallographically distinct antimony sites in Eu10Mn6Sb13 ... [more ▼]

The antimony-121 Mossbauer spectra of Eu10Mn6Sb13 have been measured between 2 and 295 K. Although the Zintl formalism indicates that the nine crystallographically distinct antimony sites in Eu10Mn6Sb13 should have formal valence states of -2, -1, 0, and +1, the Mossbauer spectral isomer shifts reveal that the valence states of the 4.0 different sites are all quite similar and correspond to an average electronic configuration for antimony of 5s(1.7)5p(4.0). This configuration corresponds to an excess of negative charge on the antimony of 0.7 or an average valence of -0.7, a valence which is rather consistent with the average antimony valence of -0.61 obtained from the Zintl formalism for the nine antimony sites in Eu10Mn6Sb13. The spectra obtained between 90 and 295 K are more consistent with the absence rather than the presence of any transferred magnetic hyperfine field at the antimony. In contrast, the spectra obtained at 2 and 5 K reveal the presence of an average transferred magnetic hyperfine field of ca. 8 T, a field that arises from the ferromagnetic ordering of the near-neighbor manganese(II) ions. [less ▲]

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See detailMagnetic susceptibility applied as an age-depth-climate relative dating technique using sediments from Scladina Cave, a Late Pleistocene cave site in Belgium
Ellwood, B. B.; Harrold, F. B.; Benoist, S. L. et al

in Journal of Archaeological Science (2004), 31(3), 283-293

Here we demonstrate that magnetic susceptibility (MS) data from Scladina Cave, Belgium, provide a time-depth-climate relationship that is correlated to the marine oxygen isotopic record and thus yields a ... [more ▼]

Here we demonstrate that magnetic susceptibility (MS) data from Scladina Cave, Belgium, provide a time-depth-climate relationship that is correlated to the marine oxygen isotopic record and thus yields a high-resolution relative dating method for sediments recovered from many archaeological sites. This methodology will help resolve one of the major problems facing archaeologists, namely the difficulty of acquiring absolute dates with reasonable precision for the period from 40,000 to 400,000 years or so. The problem is that dating techniques applicable to most materials within this age range are subject to significant errors. Relative dating techniques.. such as magnetic secular variation or stable isotope methods, offer the potential to improve this precision. but both methods suffer from problems that make broad application to many sites impossible. However, for most archaeoloaical cave sites, MS measurements of cave sediments offers the potential for intra-site correlation and paleoclimate estimation. This is possible in protected cave environments because the MS of cave sediments results from climate processes active outside caves. which cause variations in magnetic properties of the sediments that ultimately accumulate inside caves. Once deposited, these materials are often preserved and their stratigraphy provides a time-depth-climate signal that can be identified. Therefore MS data can be used as an independent methodology, alongside conventional methods such as sedimentology and palynology, for relative age dates, and correlation within and between sites by tracing evidence of paleoclimatic change. This correlation has been used to infer an age of 90,000 +/- 7000 years for Neanderthal skeletal remains recovered from Scladina Cave, an important Middle Paleolithic archaeological site in Belgium. (C) 2003 Elsevier Ltd. All rights reserved. [less ▲]

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See detailMossbauer spectral study of the magnetocaloric FeMnP1-xAsx compounds
Hermann, Raphaël ULg; Tegus, O.; Bruck, E. et al

in Physical Review b (2004), 70(21),

The magnetic phase transitions in the FeMnP1-xAsx compounds with x= 0.25, 0.35, 0.45, 0.50, and 0.55, have been studied by iron-57 Mossbauer spectroscopy. The ferromagnetic and antiferromagnetic spectra ... [more ▼]

The magnetic phase transitions in the FeMnP1-xAsx compounds with x= 0.25, 0.35, 0.45, 0.50, and 0.55, have been studied by iron-57 Mossbauer spectroscopy. The ferromagnetic and antiferromagnetic spectra have been analyzed with a model that takes into account the random distribution of the P and As near-neighbor anions of a given iron site. This distribution is a binomial distribution of the contributions to the spectra of each iron with n As near neighbors. A magnetostriction model has been used to characterize the temperature induced paramagnetic to ferromagnetic first-order phase transition and order parameters, eta(F)=2.6, 2.3, 2.0, 1.57, and 1.43 have been obtained for x=0.25, 0.35, 0.45, 0.50, and 0.55, respectively. A detailed phase diagram has been derived from the Mossbauer spectral analysis and reveals a magnetic triple point at x=similar to0.35 and similar to210 K. A model that takes into account the random binomial P and As distribution and the contribution from the iron and manganese magnetic sublattices yields excellent fits of the spectral components assigned to the ferromagnetic and incommensurate antiferromagnetic components for the x=0.25 and 0.35 compounds at all temperatures. [less ▲]

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See detailAn X-ray Rietveld, infrared, and Mossbauer spectral study of the NaMn(Fe1-xInx)(2)(PO4)(3) alluaudite-type solid solution
Hatert, Frédéric ULg; Hermann, Raphaël ULg; Long, Gary J. et al

in American Mineralogist (2003), 88(1), 211-222

Several compounds of the NaMn(Fe1-xInx)(2)(PO4)(3) solid solution were synthesized by solid state reaction in air; pure alluaudite-like compounds were obtained for x = 0.00 to 1.00. X-ray Rietveld ... [more ▼]

Several compounds of the NaMn(Fe1-xInx)(2)(PO4)(3) solid solution were synthesized by solid state reaction in air; pure alluaudite-like compounds were obtained for x = 0.00 to 1.00. X-ray Rietveld refinements indicate the presence of Na+ at the A1 and A2' sites, Mn2+ at the M1 site, and Fe2+, Fe3+, and In3+ at the M2 site. The presence of small amounts of In3+ at the M I site, and Mn2+ at the M2 site, indicates a partially disordered distribution between these cations. A good correlation was also established between the M1-M2 bond distance and the beta angle of the alluaudite-like compounds. The disordered distribution of Fe2+, Fe3+, and In3+ at the M2 site is confirmed by the broadness of the infrared absorption bands. The Mossbauer spectra, measured between 90 and 295 K, were analyzed in terms of a model that takes into account the next-nearest neighbor interactions around the M2 crystallographic site. In all cases these spectra reveal the unexpected presence of small amounts of Fe2+ at the M2 site, an amount that decreases as the In3+ content increases. The Fe2+ and Fe3+ isomer shifts are typical of the alluaudite structure and vary with temperature, as expected from a second-order Doppler shift. The derived iron vibrating masses and Mossbauer lattice temperatures are within the expected range of values for iron cations in an octahedral environment. The Fe2+ and Fe3+ quadrupole splittings are also typical of the alluaudite structure and the temperature dependence of the Fe2+ quadrupole splitting was fit with the model of Ingalls (1964), which yielded a ground state orbital splitting of ca. 380 to 570 cm(-1) for the Fe2+ sites. [less ▲]

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See detailEinstein oscillators in thallium filled antimony skutterudites
Hermann, Raphaël ULg; Jin, R. J.; Schweika, W. et al

in Physical Review Letters (2003), 90(13),

Inelastic neutron scattering measurements on several Tl filled skutterudites (Tl0.5Co3.5Fe0.5Sb12, Tl0.8Co3FeSb12, and Tl0.8Co4Sb11Sn) all show a sharp peak in the vibrational density of states at 57 ... [more ▼]

Inelastic neutron scattering measurements on several Tl filled skutterudites (Tl0.5Co3.5Fe0.5Sb12, Tl0.8Co3FeSb12, and Tl0.8Co4Sb11Sn) all show a sharp peak in the vibrational density of states at 57 +/- 2 K, which is absent in the unfilled skutterudite CoSb3. Heat capacity measurements on Tl0.8Co4Sb11Sn as compared to CoSb3 are consistent with the presence of a localized vibrational mode associated with the "rattling" thallium atoms in this filled skutterudite compound. Both results are well described by a localized Einstein mode model with an Einstein temperature Theta(E) of 53 +/- 1 K. These data provide perhaps the clearest example of local mode behavior in a concentrated metallic system. [less ▲]

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See detailMagnetic properties of iron nitride-alumina nanocomposite materials prepared by high-energy ball milling
Mishra, S. R.; Long, G. J.; Grandjean, Fernande ULg et al

in European Physical Journal D -- Atoms, Molecules, Clusters & Optical Physics (2003), 24(1-3), 93-96

The structural and magnetic properties of the granular iron nitride-alumina composite materials: (FexN)(0.2)(Al2O3)(0.8) and (FexN)(0.6)(Al2O3)(0.4), fabricated using high-energy ball milling have been ... [more ▼]

The structural and magnetic properties of the granular iron nitride-alumina composite materials: (FexN)(0.2)(Al2O3)(0.8) and (FexN)(0.6)(Al2O3)(0.4), fabricated using high-energy ball milling have been determined by using X-ray diffraction, Mossbauer spectroscopy, and magnetization measurements. The Mossbauer spectra, fit with a distribution of hyperfine fields between zero and 40 T. indicate that the weighted average field decreases with increasing milling time. The isomer shift increases with milling time because of a reduced iron 4s-electron density at the grain boundaries. Coercive fields as high as 325 and 110 Oe are obtained for (FexN)(0.2)(Al2O3)(0.8) at 5 and 300 K, respectively; the increase in the coercive field upon cooling indicates the presence of superparamagnetic particles. The coercive field increases with milling time because of the reduced particle size. The decrease in the magnetization results from the increase in both the superparamagnetic fraction and the concentration of surface defects with increased milling time. [less ▲]

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See detailEu10Mn6Sb13: A new ternary rare-earth transition-metal
Holm, A. P.; Park, S. M.; Condron, C. L. et al

in Inorganic Chemistry (2003), 42(15), 4660-4667

A new transition-metal-containing Zintl compound, Eu10Mn6Sb13, was prepared by a high-temperature Sn-flux synthesis. The structure was determined by single-crystal X-ray diffraction. Eu10Mn6Sb13 ... [more ▼]

A new transition-metal-containing Zintl compound, Eu10Mn6Sb13, was prepared by a high-temperature Sn-flux synthesis. The structure was determined by single-crystal X-ray diffraction. Eu10Mn6Sb13 crystallizes in the monoclinic space group C2/m with a = 15.1791(6) Angstrom, b = 19.1919(7) Angstrom, c = 12.2679(4) Angstrom, beta = 108.078(1)degrees, Z = 4 (R1 = 0.0410, wR2 = 0.0920), and T = 90(2) K. The structure of Eu10Mn6Sb13 is composed of double layers of Mn-centered tetrahedra separated by Eu2+ cations. The double layers are composed of edge- and corner-sharing Mn-centered tetrahedra which form cavities occupied by Eu2+ cations and [Sb-2](4-) dumbbells. Linear [Sb-3](5-) trimers bridging two tetrahedra across the cavity are also present. Bulk susceptibility data indicate paramagnetic behavior with a ferromagnetic component present below 60 K. Temperature-dependent electrical resistivity measurements show semiconducting behavior above 60 K (E-a = 0.115(2) eV), a large and unusually sharp maximum in the resistivity at similar to40 K, and metallic behavior below 40 K. Eu-151 Mossbauer spectra confirm that the europium is divalent with an average isomer shift of -11.2(1) mm/s at 100 K; the spectra obtained below 40 K reveal magnetic ordering of six of the seven europium sublattices and, at 4.2 K, complete ordering of the seven europium sublattices. [less ▲]

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See detailMagnetic and mossbauer spectral study of ErFe11Ti and ErFe11TiH
Piquer, C.; Hermann, Raphaël ULg; Grandjean, Fernande ULg et al

in Journal of Applied Physics (2003), 93(6), 3414-3421

X-ray diffraction, isothermal magnetization at 5 and 300 K, ac magnetic susceptibility measurements between 5 and 200 K, and iron-57 Mossbauer spectral measurements between 4.2 and 295 K have been carried ... [more ▼]

X-ray diffraction, isothermal magnetization at 5 and 300 K, ac magnetic susceptibility measurements between 5 and 200 K, and iron-57 Mossbauer spectral measurements between 4.2 and 295 K have been carried out on ErFe11Ti and ErFe11TiH. Hydrogen uptake has been measured by gravimetric analysis and the insertion of hydrogen into ErFe11Ti increases its magnetization, magnetic hyperfine fields, and isomer shifts as a result of the associated lattice expansion. Peaks and steplike changes in both the real and imaginary components of the ac magnetic susceptibility are observed at similar to50 and 40 K for ErFe11Ti and ErFe11TiH, respectively, and are assigned to spin-reorientation transitions resulting from the temperature dependence of the sixth-order Stevens crystal-field term of erbium. The Mossbauer spectra have been analyzed with a model which considers both these spin reorientations and the distribution of titanium atoms in the near-neighbor environment of the three crystallographically distinct iron sites. The assignment and the temperature dependencies of the hyperfine fields and isomer shifts are in complete agreement with the Wigner-Seitz cell analysis of the three iron sites in ErFe11Ti and ErFe11TiH. The changes in the hyperfine field and isomer shift with the number of titanium near neighbors of the three iron sites are in agreement with the values observed for related titanium-iron intermetallic compounds. (C) 2003 American Institute of Physics. [less ▲]

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See detailMossbauer spectral evidence for next-nearest neighbor interactions within the alluaudite structure of Na1-xLixMnFe2(PO4)(3)
Hermann, Raphaël ULg; Hatert, Frédéric ULg; Fransolet, André-Mathieu ULg et al

in Solid State Sciences (2002), 4(4), 507-513

The Mossbauer spectra of the Na1-xLixMnFe2(PO4)(3) compounds, with x = 0,00, 0.25, 0.50, and 0.75, have been measured between 90 and 295 K and analyzed in terms of a model which takes into account the ... [more ▼]

The Mossbauer spectra of the Na1-xLixMnFe2(PO4)(3) compounds, with x = 0,00, 0.25, 0.50, and 0.75, have been measured between 90 and 295 K and analyzed in terms of a model which takes into account the next-nearest neighbor interactions within the alluaudite structure. Surprisingly, the spectra reveal an unexpected presence of iron(II) in these compounds; the amount of iron(II) is observed to decrease from 19 to 15 atomic percent of the total iron content with increasing x. The temperature dependence of the Fe2+ and Fe3+ isomer shifts agrees with that expected from a second-order Doppler shift and the resulting iron vibrating masses and Mossbauer lattice temperatures are within the expected range of values for iron cations in an octahedral environment. The temperature dependence of the Fe2+ quadrupole splitting has been fit with the Ingalls' model and the results yield a ground state orbital splitting of ca. 500 cm(-1) for the iron(II) sites. The compositional dependence of the isomer shifts and Fe2+ content can be understood in terms of a decrease in the unit-cell volume with increasing substitution of sodium by lithium, a substitution which does not influence the observed quadrupole splittings. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved. [less ▲]

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See detailElectronic structure of thallium filled skutterudites studied by x-ray absorption and Mossbauer spectroscopy
Long, G. J.; Mahieu, B.; Sales, B. C. et al

in Journal of Applied Physics (2002), 92(12), 7236-7241

Thallium L-III-edge x-ray absorption and iron-57 and tin-119 Mossbauer spectral measurements have been carried out to probe the electronic structure of the three sites in the filled skutterudite TlxCo4 ... [more ▼]

Thallium L-III-edge x-ray absorption and iron-57 and tin-119 Mossbauer spectral measurements have been carried out to probe the electronic structure of the three sites in the filled skutterudite TlxCo4-yFeySb12 and TlxCo4Sb12-zSnz compounds with a range of x, y, and z values. The thallium L-III-edge x-ray absorption spectra are independent of x, y, and z and are well reproduced by full multiple scattering calculations with a cluster with a radius of 8.5 Angstrom centered on thallium. The iron-57 Mossbauer spectra consist of two doublets and the major component is assigned to iron on the cobalt sublattice in view of its hyperfine parameters. The origin of the minor component is uncertain and is tentatively assigned to either iron with thallium vacancies as next nearest neighbors or to iron in the voids. The tin-119 Mossbauer spectral hyperfine parameters clearly indicate that tin substitutes for antimony in the skutterudite structure. Further, the tin electronic configuration is very similar to that of antimony and is insensitive to the thallium content. (C) 2002 American Institute of Physics. [less ▲]

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See detailStudy of the structural, electronic, and magnetic properties of the barium-rich iron(IV) oxides, Ba2FeO4 and Ba3FeO5
Delattre, J. L.; Stacy, A. M.; Young, V. G. et al

in Inorganic Chemistry (2002), 41(11), 2834-2838

Crystals of Ba2FeO4 and Ba3FeO5, grown from a "self-sealing" KOH-Ba(OH)(2) flux, have been characterized by single-crystal X-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. Ba2FeO4 ... [more ▼]

Crystals of Ba2FeO4 and Ba3FeO5, grown from a "self-sealing" KOH-Ba(OH)(2) flux, have been characterized by single-crystal X-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. Ba2FeO4 forms nonmerohedral twinned crystals with the monoclinic space group P2(1)/c, a = 6.034(2) Angstrom, b = 7.647(2) Angstrom, c = 10.162(3) Angstrom, beta = 92.931(6)degrees, and Z = 4. Ba3FeO5 crystallizes in the orthorhombic space group Pnma, with a = 10.301(1) Angstrom, b = 8.151(1) Angstrom, c = 7.611(1) Angstrom, and Z = 4. While both compounds feature discrete FeO44- tetrahedra, the anion found in Ba2FeO4 has shorter Fe-O bonds and is significantly distorted relative to the Ba3FeO5 anion, An iron valence of 4+ was confirmed by magnet susceptibility measurements and by the low-temperature isomer shifts of -0.152 and -0.142 mm/s relative to alpha-iron for Ba2FeO4 and Ba3FeO5, respectively. [less ▲]

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See detailSynthetic, structural, magnetic, and Mossbauer spectral study of {Fe[HC(3,5-Me(2)pz)(3)](2)}I-2 and its spin-state crossover behavior
Reger, D. L.; Little, C. A.; Smith, M. D. et al

in European Journal Of Inorganic Chemistry (2002), (5), 1190-1197

The complex {Fe[HC(3,5-Me(2)pz)(3)](2)}I-2 (1) has been prepared from the reaction of FeI2 and HC(3,5-Me(2)pz)(3) (pz = pyrazolyl ring) in a 1:2 ratio. The complex is high-spin in both the solid state and ... [more ▼]

The complex {Fe[HC(3,5-Me(2)pz)(3)](2)}I-2 (1) has been prepared from the reaction of FeI2 and HC(3,5-Me(2)pz)(3) (pz = pyrazolyl ring) in a 1:2 ratio. The complex is high-spin in both the solid state and in solution at ambient temperature, In the solid state, magnetic susceptibility and Mossbauer spectral studies indicate that samples of the complex that have been crystallized and dried change completely from high-spin to low-spin upon cooling below 195 K, with a substantial two-step thermal hysteresis in the transition, The spin-crossover properties of I are sample dependent: powder samples do not change to low-spin at low temperatures. Two crystalline forms of I have been identified by X-ray crystallography, one form containing no solvent of crystallization and the other containing solvent, In both, there is only one iron site, with average Fe-N bond lengths of 2.18 and 2.17 Angstrom, values that confirm that the complex is high-spin. Single crystals of the nonsolvated form shatter at low temperatures whereas single crystals of the solvated form can be cooled to 110 K with no loss of crystallinity and remain fully high spin at this temperature, Crystallographic information: nonsolvated form is triclinic, P (1) over bar, a = 8,8062(2) Angstrom, b = 10.3549(2) Angstrom, c = 11.3549(2) Angstrom, a = 104.0768(10), beta = 110.2473(10)degrees, gamma = 92.6385(11)degrees, Z = 1; solvated form is monoclinic P2(1)/c, a 10.3214(5) Angstrom, b = 12.7753(7) Angstrom, c = 20.1995(11) Angstrom, alpha = 90degrees, beta = 97.5380(10)degrees, gamma = 90degrees, Z = 2. [less ▲]

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See detailA Magnetic and Mössbauer Spectral Study of Several Na-Mn-Fe-bearing Alluaudites
Long, Gary J.; Hautot, Dimitri; Hatert, Frédéric ULg et al

Poster (2001)

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See detailA magnetic and conversion electron Mossbauer spectral study of amorphous Dy20Fe80-yCoy thin films
Fleury-Frenette, Karl ULg; Delwiche, Jacques ULg; Grandjean, Fernande ULg et al

in IEEE Transactions on Magnetics (2001), 37(4), 2311-2314

Amorphous thin films of Dy20Fe80-yCoy, with 0 < y < 20 and of ca. 40 nm thickness, have been prepared by sputtering on polyimide substrates. The 295 K conversion electron Mossbauer spectra (CEMS) of these ... [more ▼]

Amorphous thin films of Dy20Fe80-yCoy, with 0 < y < 20 and of ca. 40 nm thickness, have been prepared by sputtering on polyimide substrates. The 295 K conversion electron Mossbauer spectra (CEMS) of these films consist of broadened sextets which have been analyzed with a distribution of hyperfine fields in which the iron moments are oriented perpendicular to the plane of the film, an orientation which is in agreement with the perpendicular magnetic anisotropy observed herein at 295 K by vibrating sample magnetrometry. The average hyperfine field and isomer shift increase linearly with increasing Co content. Both increases arise from an increase in the electron occupation of the 3d states as the cobalt content increases. [less ▲]

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