References of "Hermann, Raphaël"
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See detailThermodynamic, thermoelectric, and magnetic properties of FeSb2: A combined first-principles and experimental study
Diakhate, Momar ULg; Hermann, Raphaël ULg; Möchel, A. et al

in Physical Review. B : Condensed Matter (2011), 84(12), 125210

We analyze the thermodynamic, magnetic, and transport properties of the narrow band-gap semiconductor FeSb2 using density functional theory calculations corroborated by nuclear inelastic spectroscopy and ... [more ▼]

We analyze the thermodynamic, magnetic, and transport properties of the narrow band-gap semiconductor FeSb2 using density functional theory calculations corroborated by nuclear inelastic spectroscopy and ultrasound experiments. The vibrational properties (phonon spectrum density of states, heat capacity) and elastic constants are computed through response function calculations and are in good agreements with the measurements. The electron-phonon coupling effects are also studied. The estimations of linewidth broadening due to electron-phonon coupling along the high-symmetry directions in the first Brillouin zone are given. The linewidth broadening reaches the largest value for Fe optical modes in the vicinity of the X[0.5,0,0] point. The broadening, when compared to those obtained at the other symmetry points, differs by up to two orders of magnitude. From the Boltzmann theory applied to our electronic band structure, we investigate the electrical transport properties. It is found that a purely electronic structure description is incompatible with the record value of the Seebeck coefficient experimentally observed at T approximate to 12 K. The diamagnetic to paramagnetic crossover at a temperature around 100 K is also described from the calculation of the magnetic susceptibility, and results compare well with experiment. [less ▲]

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See detailCaractérisation et vieillissement accéléré de pigments de bleu de Prusse synthétisés selon les méthodes de préparation anciennes et modernes
Samain, Louise ULg; Lauricella, Melina; Silversmit, Geert et al

Conference (2011, April 11)

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See detailLattice dynamics in the thermoelectric Zintl compound Yb14MnSb11
Möchel, A.; Sergueev, I.; Wille, H.-C. et al

in Physical Review (2011), 84(18),

The density of phonon states in the thermoelectric material Yb14MnSb11 has been studied first by inelastic neutron scattering and second in an element-specific way by nuclear inelastic x-ray scattering ... [more ▼]

The density of phonon states in the thermoelectric material Yb14MnSb11 has been studied first by inelastic neutron scattering and second in an element-specific way by nuclear inelastic x-ray scattering. The low sound velocity of 1880(50) m/s as obtained from the density of phonon states can be identified as an important reason for the low heat transport in this system. The high melting temperature of Yb14MnSb11 contrasts with the low energy of all phonons (<25 meV) and relates to an unusual lack of softening of phonon modes with temperature, when comparing the phonon density of states observed at ambient temperatures and at 1200 K. We have also measured the density of phonon states of the related Eu14MnSb11 compound and of the thermoelectric Zintl phase Zn4Sb3 in order to compare with related thermodynamic properties of Yb14MnSb11 and to elucidate the different mechanisms of the heat conductivity reduction in Zintl phases. [less ▲]

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See detailLattice dynamics in the FeSb3 skutterudite
Moechel, A.; Sergueev, I.; Long, Gary J. et al

in Physical Review (2011), 84(6),

Thin films of FeSb3 were characterized by electronic transport magnetometry, x-ray diffraction, Fe-57 and Sb-121 nuclear inelastic scattering, and Fe-57 Mossbauer spectroscopy. Resistivity and ... [more ▼]

Thin films of FeSb3 were characterized by electronic transport magnetometry, x-ray diffraction, Fe-57 and Sb-121 nuclear inelastic scattering, and Fe-57 Mossbauer spectroscopy. Resistivity and magnetometry measurements reveal semiconducting behavior with a 16.3(4) meV band gap and an effective paramagnetic moment of 0.57(6) mu(B) respectively. A systematic comparison of the lattice dynamics with CoSb3 and EuFe4Sb12 reveals that the Fe4Sb12 framework is softer than the Co4Sb12 framework, and that the observed softening and the associated lowering of the lattice thermal conductivity in the RFe4Sb12 filled skutterudites are not only related to the filler but also to the Fe4Sb12 framework. [less ▲]

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See detailLocal ordering and magnetism in Ga0.9Fe3.1N
Burghaus, Jens; Sougrati, Moulay T.; Moechel, Anne et al

in Journal of Solid State Chemistry (2011), 184(9), 2315-2321

Prior investigations of the ternary nitride series Ga1-xFe3+xN (0 <= x 1) have indicated a transition from ferromagnetic gamma'-Fe4N to antiferromagnetic ``GaFe3N''. The ternary nitride ``GaFe3N'' has ... [more ▼]

Prior investigations of the ternary nitride series Ga1-xFe3+xN (0 <= x 1) have indicated a transition from ferromagnetic gamma'-Fe4N to antiferromagnetic ``GaFe3N''. The ternary nitride ``GaFe3N'' has been magnetically and spectroscopically reinvestigated in order to explore the weakening of the ferromagnetic interactions through the gradual incorporation of gallium into gamma'-Fe4N. A hysteretic loop at RI reveals the presence of a minority phase of only 0.1-0.2 at\%, in accord with the sound two-step synthesis. The composition of the gallium-richest phase ``GaFe3N'' was clarified by Prompt Gamma-ray Activation Analysis and leads to the berthollide formula Ga0.91(1)Fe3.09(10)N1.05(7). Magnetic measurements indicate a transition around 8 K, further supported by Mossbauer spectral data. The weakening of the ferromagnetic coupling through an increasing gallium concentration is explained by a simple Stoner argument. In Ga0.9Fe3.1N the presence of iron on the gallium site affects the magnetism by the formation of 13-atom iron clusters. (C) 2011 Elsevier Inc. All rights reserved. [less ▲]

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See detailShape Induced Symmetry in Self-Assembled Mesocrystals of Iron Oxide Nanocubes
Disch, Sabrina; Wetterskog, Erik; Hermann, Raphaël ULg et al

in Nano Letters (2011), 11(4), 1651-1656

Grazing incidence small-angle scattering,and electron microscopy have been used to show for the first time that nonspherical nanoparticles can assemble into highly ordered body-centered tetragonal ... [more ▼]

Grazing incidence small-angle scattering,and electron microscopy have been used to show for the first time that nonspherical nanoparticles can assemble into highly ordered body-centered tetragonal mesocrystals. Energy models accounting for the directionality and magnitude of the van der Waals and dipolar interactions as a function of the degree of truncation of the nanocubes illustrated the importance of the directional dipolar forces for the formation of the initial nanocube clusters and the dominance of the van der Waals multibody interactions in the dense packed arrays. [less ▲]

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See detailPhase-Change Materials: Vibrational Softening upon Crystallization and Its Impact on Thermal Properties
Matsunaga, Toshiyuki; Yamada, Noboru; Kojima, Rie et al

in Advanced Functional Materials (2011), 21(12), 2232-2239

Crystallization of an amorphous solid is usually accompanied by a significant change of transport properties, such as an increase in thermal and electrical conductivity. This fact underlines the ... [more ▼]

Crystallization of an amorphous solid is usually accompanied by a significant change of transport properties, such as an increase in thermal and electrical conductivity. This fact underlines the importance of crystalline order for the transport of charge and heat. Phase-change materials, however, reveal a remarkably low thermal conductivity in the crystalline state. The small change in this conductivity upon crystallization points to unique lattice properties. The present investigation reveals that the thermal properties of the amorphous and crystalline state of phase-change materials show remarkable differences such as higher thermal displacements and a more pronounced anharmonic behavior in the crystalline phase. These findings are related to the change of bonding upon crystallization, which leads to an increase of the sound velocity and a softening of the optical phonon modes at the same time. [less ▲]

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See detailProperties of spark plasma sintered nanostructured Zn1+xSb
Birkel, Christina S.; Claudio, Tania; Panthoefer, Martin et al

in Physica Status Solidi A. Applications and Materials Science (2011), 208(8), 1913-1919

Engineering materials with specific physical properties has recently focused on the effect of nanoscopic inhomogeneities at the 10 nm scale. Such features are expected to scatter medium and long ... [more ▼]

Engineering materials with specific physical properties has recently focused on the effect of nanoscopic inhomogeneities at the 10 nm scale. Such features are expected to scatter medium and long-wavelength phonons lowering thereby the thermal conductivity of the system without simultaneously decreasing the charge transport (phonon-glass electron-crystal concept). A new Zn1+xSb nanophase obtained by a wet chemical approach was densified by spark plasma sintering (SPS). Investigations on compounds subsumed as ``Zn4Sb3'' always suffer from its low thermal stability and the contamination of the nanoparticles with solvents and additives used in the synthesis. In order to gain insight into this compound's electronic properties we investigated a material free from remnants of the synthesis but contaminated with a small amount of well-characterized decomposition product, i.e., ZnSb. To investigate the influence of the sintering process on the densified samples, different SPS conditions were applied. Four different conditions were used with heating rates between 160 degrees and 230 degrees C/min, sintering temperatures between 130 and 190 degrees C and sintering times between 3 and 6 min. Powders from the surface of the pellets were subject to powder X-ray diffraction (XRD) yielding information about the surface composition. Small pieces of the pellets were also characterized using high-energy synchrotron radiation scattering in order to reveal the phase compositions inside the pellets. Small changes in the sintering conditions of the samples were found to have a large influence on the resulting sample compositions. In addition, the phase compositions on the surface differ significantly from the ones inside the pellets which show a much higher grade of decomposition. The density and morphology of the obtained pellets have been investigated by means of laser microscopy and scanning electron microscopy (SEM). The low density and porosity of the different pellets is a result of the graphite pressing tool which has to be used to ensure the temperature control during the SPS process. (C) 2011 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim [less ▲]

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See detailMilli-electronvolt monochromatization of hard X-rays with a sapphire backscattering monochromator
Sergueev, I.; Wille, H.-C.; Hermann, Raphaël ULg et al

in Journal of Synchrotron Radiation (2011), 18(Part 5), 802-810

A sapphire backscattering monochromator with 1.1 (1) meV bandwidth for hard X-rays (20-40 keV) is reported. The optical quality of several sapphire crystals has been studied and the best crystal was ... [more ▼]

A sapphire backscattering monochromator with 1.1 (1) meV bandwidth for hard X-rays (20-40 keV) is reported. The optical quality of several sapphire crystals has been studied and the best crystal was chosen to work as the monochromator. The small energy bandwidth has been obtained by decreasing the crystal volume impinged upon by the beam and by choosing the crystal part with the best quality. The monochromator was tested at the energies of the nuclear resonances of (121)Sb at 37.13 keV, (125)Te at 35.49 keV, (119)Sn at 23.88 keV, (149)Sm at 22.50 keV and (151)Eu at 21.54 keV. For each energy, specific reflections with sapphire temperatures in the 150-300 K region were chosen. Applications to nuclear inelastic scattering with these isotopes are demonstrated. [less ▲]

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See detailWet Chemical Synthesis and a Combined X-ray and Mossbauer Study of the Formation of FeSb2 Nanoparticles
Birkel, Christina S.; Kieslich, Gregor; Bessas, Dimitrios et al

in Inorganic Chemistry (2011), 50(22), 11807-11812

Understanding how solids form is a challenging task, and few strategies allow for elucidation of reaction pathways that are useful for designing the synthesis of solids. Here, we report a powerful ... [more ▼]

Understanding how solids form is a challenging task, and few strategies allow for elucidation of reaction pathways that are useful for designing the synthesis of solids. Here, we report a powerful solution-mediated approach for formation of nanocrystals of the thermoelectrically promising FeSb2 that uses activated metal nanoparticles as precursors. The small particle size of the reactants ensures minimum diffusion paths, low activation barriers, and low reaction temperatures, thereby eliminating solid-solid diffusion as the rate-limiting step in conventional bulk-scale solid-state synthesis. A time- and temperature-dependent study of formation of nanoparticular FeSb2 by X-ray powder diffraction and iron-57 Mossbauer spectroscopy showed the incipient format on of the binary phase in the temperature range of 200-250 degrees C. [less ▲]

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See detailLattice dynamics and anomalous softening in the YbFe4Sb12 skutterudite
Moechel, A.; Sergueev, I.; Wille, H.-C. et al

in Physical Review (2011), 84(18),

The lattice dynamics of the filled skutterudite YbFe4Sb12 was studied by resonant ultrasound spectroscopy and an anomalous softening in the temperature dependence of the elastic constants at similar to 50 ... [more ▼]

The lattice dynamics of the filled skutterudite YbFe4Sb12 was studied by resonant ultrasound spectroscopy and an anomalous softening in the temperature dependence of the elastic constants at similar to 50 K was observed. This anomaly can not be explained by the dynamics of the filler, in contrast to other filled skutterudites. We have further investigated the origin of this anomaly using macroscopic and microscopic measurements. A rearrangement of the spectral weight of the Yb phonon states was observed in the temperature dependence of the density of phonon states, obtained by inelastic neutron scattering. We suggest that the anomaly is due to a change of the Yb valence state and that the anomaly and the phonon spectral weight rearrangement have the same origin. [less ▲]

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See detailSpin correlations in the extended kagome system YBaCo3FeO7
Valldor, Martin; Hermann, Raphaël ULg; Wuttke, Joachim et al

in Physical Review. B : Condensed Matter (2011), 84(22),

The transition metal-based oxide YBaCo3FeO7 is structurally related to the mineral Swedenborgite SbNaBe4O7, a polar noncentrosymmetric crystal system. The magnetic Co3Fe sublattice consists of a ... [more ▼]

The transition metal-based oxide YBaCo3FeO7 is structurally related to the mineral Swedenborgite SbNaBe4O7, a polar noncentrosymmetric crystal system. The magnetic Co3Fe sublattice consists of a tetrahedral network containing kagome-like layers with trigonal interlayer sites. This geometry causes frustration effects for magnetic ordering, which were investigated by magnetization measurements, Mossbauer spectroscopy polarized neutron diffraction, and neutron spectroscopy. Magnetization measurement and neutron diffraction do not show long range ordering even at low temperature (1 K), although a strong antiferromagnetic coupling (similar to 2000 K) is deduced from the magnetic susceptibility. Below 590 K we observe two features, a spontaneous weak anisotropic magnetization hysteresis along the polar crystallographic axis and a hyperfine field on the Fe kagome sites, whereas the Fe spins on the interlayer sites remain idle. Below similar to 50 K the onset of a hyperfine field shows the development of moments static on the Mossbauer time scale also for the Fe interlayer sites. Simultaneously, an increase of spin correlations is found by polarized neutron diffraction. The relaxation part of the dynamic response has been further investigated by high-resolution neutron spectroscopy, which reveals that the spin correlations start to freeze below similar to 50 K. Monte Carlo simulations show that the neutron scattering results at lower temperatures are compatible with a recent proposal that the particular geometric frustration in the Swedenborgite structure promotes quasi-one-dimensional partial order. [less ▲]

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See detailMicrostructures and nanostructures in long-term annealed AgPb18SbTe20 (LAST-18) compounds and their influence on the thermoelectric properties
Dadda, Jayaram; Mueller, Eckhard; Perlt, Susanne et al

in Journal of Materials Research (2011), 26(15), 1800-1812

This article reports on the role of annealing on the development of microstructure and its concomitant effects on the thermoelectric 18 lead-antimony-silver- tellurium, LAST-18) compounds. The annealing ... [more ▼]

This article reports on the role of annealing on the development of microstructure and its concomitant effects on the thermoelectric 18 lead-antimony-silver- tellurium, LAST-18) compounds. The annealing temperature was varied by applying a gradient annealing method, where a 40-mm-long sample rod was heat treated in an axial temperature gradient spanning between 200 and 600 degrees C for 7 days. Transmission electron microscopy investigations revealed Ag2Te nanoparticles at a size of 20-250 nm in the matrix. A remarkable reduction in the thermal conductivity to as low as 0.8W/mK was also recorded. The low thermal conductivity coupled with a large Seebeck coefficient of similar to 320 mu V/K led to high ZT of about 1.05 at 425 degrees C for the sample annealed at 505 degrees C. These results also demonstrate that samples annealed above 450 degrees C for long term are more thermally stable than those treated at lower temperatures. [less ▲]

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See detailFading of modern Prussian blue pigments in linseed oil medium
Samain, Louise ULg; Silversmit, Geert; Sanyova, Jana et al

in Journal of Analytical Atomic Spectrometry [=JAAS] (2011), 26(5), 930

The fading of modern laboratory-synthesized and commercial Prussian blue, iron(III) hexacyanoferrate(II), based pigments in a linseed oil medium during exposure to light has been investigated. The ... [more ▼]

The fading of modern laboratory-synthesized and commercial Prussian blue, iron(III) hexacyanoferrate(II), based pigments in a linseed oil medium during exposure to light has been investigated. The Prussian blue pigments were painted from linseed oil, as a pure pigment and mixed with white lead, (PbCO3)2Pb(OH)2, zinc white, ZnO, or titanium white, TiO2, pigment. The samples were subjected to accelerated ageing for 800 hours and the light fastness of the Prussian blue pigment was evaluated by reference to blue wool standards. Pure Prussian blue is extremely light fast whilst it strongly fades when mixed with a white pigment, especially with lead white or zinc oxide. The painted samples were studied by UV-visible, iron K-edge X-ray absorption, iron-57 transmission Mössbauer, and attenuated total reflectance infrared spectroscopy. X-ray absorption results reveal a decrease in the iron coordination number in aged samples in the presence of white pigment. The Mössbauer spectra of the pure Prussian blue and the unaged and aged mixtures of Prussian blue and lead white or zinc oxide at 1:100 and 1:10 dilution ratios, respectively, indicate the presence of iron(II) and iron(III) in a ratio close to one as expected for the bulk stoichiometric KFeIII[FeII(CN)6]; no change in the spectral parameters was observed upon ageing. Combined with the X-ray near edge absorption and infrared studies, these results suggest reduction of the surface iron ions in the Prussian blue with ageing upon exposure to light. [less ▲]

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See detailNMR relaxation and magnetic properties of superparamagnetic nanoworms
Gossuin, Yves; Disch, Sabrina; Vuong, Quoc L. et al

in Contrast Media & Molecular Imaging (2010), 5(6), 318-322

Maghemite particles are used as T-2 contrast agents for magnetic resonance imaging, especially for molecular and cellular imaging. Linear clusters of particles - called nanoworms - were recently developed ... [more ▼]

Maghemite particles are used as T-2 contrast agents for magnetic resonance imaging, especially for molecular and cellular imaging. Linear clusters of particles - called nanoworms - were recently developed to enhance the targeting efficiency. In this work, the magnetic and NMR relaxation properties of these nanoworms are studied at multiple magnetic fields. After the usual saturation at 0.5 T, the magnetization of the worms is still increasing, which results in an appreciable increase of the transverse relaxivity at high magnetic fields. The obtained relaxivities are typical of superparamagnetic particles of iron oxide (SPIOs). The transverse relaxation of the worms is clearly more efficient than for the isolated grains, which is confirmed by computer simulations. At high field, the longitudinal relaxation of the worms is less pronounced than for the grains, as expected for SPIOs. The nanoworms thus constitute a promising T-2 agent for cellular and molecular imaging. Copyright (C) 2010 John Wiley Sons, Ltd. [less ▲]

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See detailA study of low-energy guest phonon modes in clathrate-II NaxSi136 (x = 3, 23, and 24)
Beekman, M.; Hermann, Raphaël ULg; Möchel, Anne ULg et al

in Journal of Physics : Condensed Matter (2010)

Single-crystal x-ray diffraction from clathrate-II NaxSi136 (x = 24) prepared by a new technique reveals the exceptionally large Na@Si-28 atomic displacement parameter (U-eq) is strongly temperature ... [more ▼]

Single-crystal x-ray diffraction from clathrate-II NaxSi136 (x = 24) prepared by a new technique reveals the exceptionally large Na@Si-28 atomic displacement parameter (U-eq) is strongly temperature dependent, and can be attributed to low-energy rattling modes associated with the Na guest. Inelastic neutron scattering (INS) spectra collected from NaxSi136 powder specimens (x = 3, 23) confirm the presence of low-energy guest-derived phonon modes for Na@Si-28 and Na@Si-20. The lower energy Na@Si-28 rattler mode falls in the frequency range of the silicon host acoustic phonons, indicating the possibility for interaction with these phonons. The presence of these low-energy modes combined with the ability to controllably vary the guest content presents a unique opportunity for exploring the influence of guest-framework interactions on the lattice dynamics in intermetallic clathrates. [less ▲]

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See detailNuclear forward and inelastic spectroscopy on 125Te and Sb2 125Te3 2
Wille, H.-C.; Hermann, Raphaël ULg; Sergueev, I. et al

in Europhysics Letters [=EPL] (2010)

We report on the observation of nuclear forward and nuclear inelastic scattering of synchrotron radiation by Te-125 and the application of both spectroscopic methods to tellurium compounds by using a high ... [more ▼]

We report on the observation of nuclear forward and nuclear inelastic scattering of synchrotron radiation by Te-125 and the application of both spectroscopic methods to tellurium compounds by using a high-resolution backscattering sapphire monochromator in combination with fast detection electronics. The lifetime of the nuclear resonance and the energy of the transition were determined to be 2.131(12) ns and 35493.12(30) eV, respectively. As applications, the nuclear inelastic spectrum in Sb2Te3 and the nuclear forward scattering by Te metal were measured. These measurements open the field of nuclear resonance spectroscopy on tellurium compounds such as thermoelectric and superconducting materials. [less ▲]

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See detailElectronic Control of Spin Coupling in Keplerate-Type Polyoxomolybdates
Botar, Bogdan; Ellern, Arkady; Hermann, Raphaël ULg et al

in Angewandte Chemie International Edition (2009), 48(48), 9080-9083

We recently identified a synthetic procedure for the isolation of Keplerate structures based on the reaction of multivalent heterometal centers with larger polyoxomolybate(V/VI) units that coexist in a ... [more ▼]

We recently identified a synthetic procedure for the isolation of Keplerate structures based on the reaction of multivalent heterometal centers with larger polyoxomolybate(V/VI) units that coexist in a reaction solution at a certain pH. This approach yielded Keplerate clusters of the type {Mo72Mo8V22},[16] {Mo72V15Fe7Mo8}, and {Mo72V11Fe11Mo8},[14] which were obtained as kinetic products within minutes to a few hours following addition of KCl. Herein, we demonstrate for an analogous reaction system, how novel {Mo72Fe30} Keplerate species with partially reduced {(Mo)Mo5} building blocks (Robin–Day class III) can be identified, based on Raman spectroscopy time profiles of acidified aqueous molybdate reaction solutions. [less ▲]

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See detailInfluence of the rare-earth element on the effects of the structural and magnetic phase transitions in CeFeAsO, PrFeAsO and NdFeAsO
McGuire, Michael A; Hermann, Raphaël ULg; Sefat, Athena S et al

in New Journal of Physics (2009), 11

We present results of transport and magnetic properties and heat capacity measurements on polycrystalline CeFeAsO, PrFeAsO and NdFeAsO. These materials undergo structural phase transitions, spin density ... [more ▼]

We present results of transport and magnetic properties and heat capacity measurements on polycrystalline CeFeAsO, PrFeAsO and NdFeAsO. These materials undergo structural phase transitions, spin density wave-like magnetic ordering of small moments on iron and antiferromagnetic ordering of rare-earth moments. The temperature dependence of the electrical resistivity, Seebeck coefficient, thermal conductivity, Hall coefficient and magnetoresistance are reported. The magnetic behavior of the materials have been investigated using Mossbauer spectroscopy and magnetization measurements. Transport and magnetic properties are affected strongly by the structural and magnetic transitions, suggesting significant changes in the band structure and/or carrier mobilities occur, and phonon-phonon scattering is reduced upon transformation to the low-temperature structure. Results are compared with recent reports for LaFeAsO, and systematic variations in properties as the identity of Ln is changed are observed and discussed. As Ln progresses across the rare-earth series from La to Nd, an increase in the hole contributions to the Seebeck coefficient and increases in magnetoresistance and the Hall coefficient are observed in the low-temperature phase. Analysis of hyperfine fields at the iron nuclei determined from Mossbauer spectra indicates that the moment on Fe in the orthorhombic phase is nearly independent of the identity of Ln, in apparent contrast to reports of powder neutron diffraction refinements. [less ▲]

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See detailA structural, magnetic and Mössbauer spectral study of the magnetocaloric Mn1.1Fe0.9P1-xGex compounds
Sougrati, Moulay Tahar ULg; Hermann, Raphaël ULg; Grandjean, Fernande ULg et al

in Journal of Physics : Condensed Matter (2008), 20

The structural, magnetic and Mössbauer spectral properties of the magnetocaloric Mn1.1Fe0.9P1−xGex compounds, with 0.19 < x < 0.26, have been measured between 4.2 and 295 K. The 295 K unit-cell volume ... [more ▼]

The structural, magnetic and Mössbauer spectral properties of the magnetocaloric Mn1.1Fe0.9P1−xGex compounds, with 0.19 < x < 0.26, have been measured between 4.2 and 295 K. The 295 K unit-cell volume increases from x = 0.19 to 0.22 and is substantially smaller in the ferromagnetic Mn1.1Fe0.9P0.74Ge0.26. The temperature dependence of the magnetization reveals a ferromagnetic to paramagnetic transition with a Curie temperature between approximately 250 and 330 K and hysteresis width of 10 to 4 K, for 0.19 < x < 0.25. The composition Mn1.1Fe0.9P0.78Ge0.22 shows the largest isothermal entropy change of approximately 10 J/(kgKT) at 290 K. The M¨ossbauer spectra have been analysed with a binomial distribution of hyperfine fields correlated with a change in isomer shift and quadrupole shift, a distribution that results from the distribution of phosphorus and germanium among the near neighbours of the iron. The coexistence of paramagnetic and magnetically ordered phases in ranges of temperature of up to 50 K around the Curie temperature is observed in the Mössbauer spectra and is associated with the first-order character of the ferromagnetic to paramagnetic transition. The temperature dependence of the weighted average hyperfine field is well fitted within the magnetostrictive model of Bean and Rodbell. Good fits of the Mössbauer spectra could only be achieved by introducing a difference between the isomer shifts in the paramagnetic and ferromagnetic phases, a difference that is related to the magnetostriction and electronic structure change. [less ▲]

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