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See detailLinear electro-optic effect in multiferroic BiFeO3 thin films
Sando, D.; Hermet, Patrick ULg; Allibe, J. et al

in Physical Review B (2014), 89

Multiferroics are materials with coexisting magnetic and ferroelectric orders, which show potential for electrically controlled spintronic devices. A common application of ferroelectrics is in electro ... [more ▼]

Multiferroics are materials with coexisting magnetic and ferroelectric orders, which show potential for electrically controlled spintronic devices. A common application of ferroelectrics is in electro-optical modulators exploiting their electric-field-dependent optical indices. The coupling of optical and magnetic degrees of freedom is attractive for designing multifunctional devices, but to date the electro-optical response of multiferroics has hardly been explored. Here we report a joint experimental and theoretical study of this effect in multiferroic BiFeO3 thin films. We confirm the large birefringence present in single crystals and determine the electro-optic coefficients r13 and r33. We present approaches to increase the obtained coefficients, for instance, by using tetragonal-like BiFeO3, and expand the potential of multiferroics to optical applications. [less ▲]

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See detailGeometric ferroelectricity in fluoroperovskites
Garcia-Castro, A. C.; Spaldin, Nicola A.; Romero, A. H. et al

in Physical Review B (2014), 89

We used first-principles calculations to investigate the existence and origin of the ferroelectric instability in the ABF3 fluoroperovskites. While the ground states of most ABF3 compounds are ... [more ▼]

We used first-principles calculations to investigate the existence and origin of the ferroelectric instability in the ABF3 fluoroperovskites. While the ground states of most ABF3 compounds are paraelectric (Pnma phase), we find that many fluoroperovskites have a ferroelectric instability in their high-symmetry cubic structure that is of similar amplitude to that commonly found in oxide perovskites. In contrast to the oxides, however, the fluorides have nominal Born effective charges, indicating a different mechanism for the instability.We show that the instability originates from ionic size effects, and is therefore in most cases largely insensitive to pressure and strain, again in contrast to the oxide perovskites. An exception is NaMnF3, where coherent epitaxial strain matching to a substrate with equal in-plane lattice constants destabilizes the bulk Pnma structure, leading to a ferroelectric, and indeed multiferroic, ground state with an unusual polarization/strain response. [less ▲]

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See detailDoping-dependent band structure of LaAlO3/SrTiO3 interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission
Cancellieri, C.; Reinle-Schmitt, M.L.; Kobayashi, M. et al

in Physical Review B (2014), 89

Polarization-controlled synchrotron radiation was used to map the electronic structure of buried conducting interfaces of LaAlO3/SrTiO3 in a resonant angle-resolved photoemission experiment. A strong ... [more ▼]

Polarization-controlled synchrotron radiation was used to map the electronic structure of buried conducting interfaces of LaAlO3/SrTiO3 in a resonant angle-resolved photoemission experiment. A strong polarization dependence of the Fermi surface and band dispersions is demonstrated, highlighting different Ti 3d orbitals involved in two-dimensional (2D) conduction. Measurements on samples with different doping levels reveal different band occupancies and Fermi-surface areas.The photoemission results are directly compared with advanced first-principles calculations, carried out for different 3d-band filling levels connected with the 2D mobile carrier concentrations obtained from transport measurements, with indication of charge localization at the interface. [less ▲]

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See detailVibrational properties and stabilization mechanism of the amorphous phase of doped GeTe
Raty, Jean-Yves ULg; Noé, Pierre; Ghezzi, G. et al

in Physical Review B (2013), 88(1),

Doping chalcogenide phase change materials was shown to improve the stability of the amorphous phase at high temperature and to strongly increase the crystallization temperature. In this work, we use ab ... [more ▼]

Doping chalcogenide phase change materials was shown to improve the stability of the amorphous phase at high temperature and to strongly increase the crystallization temperature. In this work, we use ab initio molecular dynamics together with Fourier transform infrared spectroscopy to address the stabilization of GeTe doped with nitrogen and carbon in the amorphous phase. The comparison between the simulation and experimental results allows in-depth understanding of the mechanisms. The inclusion of C and N leads to an increase in high frequency vibrational modes and to a lowering of the boson peak intensity. The reduction of the density of floppy vibrational modes and the computed increase of the mechanical rigidity are responsible for the higher activation energy for crystallization. The mechanism described here could apply more generally to stabilize other Ge-Sb-Te phase change materials and ionocovalent glasses at high temperature. © 2013 American Physical Society. [less ▲]

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See detailLattice instabilities in bulk EuTiO3
Bessas, D.; Rushchanskii, K. Z.; Kachlik, M. et al

in PHYSICAL REVIEW B (2013), 88(14),

The phase purity and the lattice dynamics in bulk EuTiO3 were investigated both microscopically, using x-ray and neutron diffraction, Eu-151-Mossbauer spectroscopy, and Eu-151 nuclear inelastic scattering ... [more ▼]

The phase purity and the lattice dynamics in bulk EuTiO3 were investigated both microscopically, using x-ray and neutron diffraction, Eu-151-Mossbauer spectroscopy, and Eu-151 nuclear inelastic scattering, and macroscopically using calorimetry, resonant ultrasound spectroscopy, and magnetometry. Furthermore, our investigations were corroborated by ab initio theoretical studies. The perovskite symmetry, Pm (3) over barm, is unstable at the M- and R-points of the Brillouin zone. The lattice instabilities are lifted when the structure relaxes in one of the symmetries: I4/mcm, Imma, R (3) over barc with relative relaxation energy around -25 meV. Intimate phase analysis confirmed phase purity of our ceramics. A prominent peak in the Eu specific density of phonon states at 11.5 meV can be modeled in all candidate symmetries. A stiffening on heating around room temperature is indicative of a phase transition similar to the one observed in SrTiO3, however, although previous studies reported the structural phase transition to the tetragonal I4/mcm phase our detailed sample purity analysis and thorough structural studies using complementary techniques did not confirm a direct phase transition. Instead, in the same temperature range, Eu delocalization is observed which might explain the lattice dynamical instabilities. [less ▲]

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See detailEffect of pressure, temperature, fluorine doping, and rare earth elements on the phonon density of states of LFeAsO studied by nuclear inelastic scattering
Sergueev, I.; Hermann, Raphael ULg; Bessas, D. et al

in PHYSICAL REVIEW B (2013), 87(6), 064302-9

We have performed systematic studies of the lattice dynamics in LFeAsO (L = La, Ce, Pr, Nd, Sm) in the parent and in the similar to 10% F-doped compounds as a function of pressure and temperature. We have ... [more ▼]

We have performed systematic studies of the lattice dynamics in LFeAsO (L = La, Ce, Pr, Nd, Sm) in the parent and in the similar to 10% F-doped compounds as a function of pressure and temperature. We have found that the modifications in the partial Fe density of phonon states are mainly governed by the Fe-As bond length. The change of this bond length explains the change of the Fe density of phonon states above 25 meV. We further observe anomalies in the behavior of the phonon mode near 16 meV. In the parent phase, this mode softens anomalously upon cooling through the structural phase transition. Upon F doping, this mode hardens indicating a strong electron-phonon coupling. This suggests that the corresponding phonons play an important role in the competition between superconductivity and magnetism in these materials. DOI: 10.1103/PhysRevB.87.064302 [less ▲]

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See detailElectric control of the magnetization in BiFeO3/LaFeO3 superlattices
Zanolli, Zeila ULg; Wojdeł, Jacek; Iniguez, Jorge et al

in Physical Review B (2013), 88

First-principles techniques are used to investigate the behavior of BiFeO3/LaFeO3 perovskite oxide superlattices epitaxially grown on a (001)-SrTiO3 substrate. The calculations show that 1/1 superlattices ... [more ▼]

First-principles techniques are used to investigate the behavior of BiFeO3/LaFeO3 perovskite oxide superlattices epitaxially grown on a (001)-SrTiO3 substrate. The calculations show that 1/1 superlattices exhibit a Pmc21 ground state combining a trilinear coupling of one polar and two oxygen rotational lattice modes, and weak ferromagnetism. The microscopic mechanism allowing one to manipulate the magnetization with an electric field in such systems is presented and its dependence on strain and chemical substitution is discussed. BiFeO3/LaFeO3 artificial superlattices appear to be good candidates to achieve electric switching of magnetization at room temperature. [less ▲]

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See detailPhenomenological thermodynamic potential for CaTiO3 single crystals
Gu, Yijia; Rabe, Karin; Bousquet, Eric ULg et al

in Physical Review B (2012), 85

The antiferrodistortive (AFD) structural transitions of calcium titanate (CaTiO3) at ambient pressure have been extensively studied during the last few years. It has been found that none of the AFD ... [more ▼]

The antiferrodistortive (AFD) structural transitions of calcium titanate (CaTiO3) at ambient pressure have been extensively studied during the last few years. It has been found that none of the AFD polymorphs is polar or ferroelectric. However, it was recently shown theoretically and later experimentally confirmed that a ferroelectric transition in CaTiO3 can be induced by tensile strains. The ferroelectric instability is believed to be strongly coupled to the AFD soft modes. In this paper, we present a complete thermodynamic potential for describing the coupling between the AFD and ferroelectric phase transitions. We analyzed the dependence of transition temperatures on stress and strain condition. Based on this potential, a (001) CaTiO3 thin film diagram was constructed. The results show good agreement with available experimental observations. The strong suppression of ferroelectric transition by the AFD transition is discussed. [less ▲]

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See detailLattice dynamics in Bi2Te3 and Sb2Te3: Te and Sb density of phonon states
Bessas, D.; Sergueev, I.; Wille, H.-C. et al

in PHYSICAL REVIEW B (2012), 86(22), 224301-9

The lattice dynamics in Bi2Te3 and Sb2Te3 were investigated both microscopically and macroscopically using Sb-121 and Te-125 nuclear inelastic scattering, x-ray diffraction, and heat capacity measurements ... [more ▼]

The lattice dynamics in Bi2Te3 and Sb2Te3 were investigated both microscopically and macroscopically using Sb-121 and Te-125 nuclear inelastic scattering, x-ray diffraction, and heat capacity measurements. In combination with earlier inelastic neutron scattering data, the element-specific density of phonon states was obtained for both compounds and phonon polarization analysis was carried out for Bi2Te3. A prominent peak in the Te specific density of phonon states at 13 meV, that involves mainly in-plane vibrations, is mostly unaffected upon substitution of Sb with Bi revealing vibrations with essentially Te character. A significant softening is observed for the density of vibrational states of Bi with respect to Sb, consistently with the mass homology relation in the long-wavelength limit. In order to explain the energy mismatch in the optical phonon region, a similar to 20% force constant softening of the Sb-Te bond with respect to the Bi-Te bond is required. The reduced average speed of sound at 20 K in Bi2Te3, 1.75(1) km/s, compared to Sb2Te3, 1.85(4) km/s, is not only related to the larger mass density but also to a larger Debye level. The observed low lattice thermal conductivity at 295 K, 2.4 Wm(-1)K(-1) for Sb2Te3 and 1.6 Wm(-1)K(-1) for Bi2Te3, cannot be explained by anharmonicity alone given the rather modest Gruneisen parameters, 1.7(1) for Sb2Te3 and 1.5(1) for Bi2Te3, without accounting for the reduced speed of sound and more importantly the low acoustic cutoff energy. [less ▲]

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See detailDensity of states of chaotic Andreev billiards
Kuipers, Jack; Engl, Thomas; Berkolaiko, Gregory et al

in PHYSICAL REVIEW B (2011), 83(19), 195316-21

Quantum cavities or dots have markedly different properties depending on whether their classical counterparts are chaotic or not. Connecting a superconductor to such a cavity leads to notable proximity ... [more ▼]

Quantum cavities or dots have markedly different properties depending on whether their classical counterparts are chaotic or not. Connecting a superconductor to such a cavity leads to notable proximity effects, particularly the appearance, predicted by random matrix theory, of a hard gap in the excitation spectrum of quantum chaotic systems. Andreev billiards are interesting examples of such structures built with superconductors connected to a ballistic normal metal billiard since each time an electron hits the superconducting part it is retroreflected as a hole (and vice versa). Using a semiclassical framework for systems with chaotic dynamics, we show how this reflection, along with the interference due to subtle correlations between the classical paths of electrons and holes inside the system, is ultimately responsible for the gap formation. The treatment can be extended to include the effects of a symmetry-breaking magnetic field in the normal part of the billiard or an Andreev billiard connected to two phase-shifted superconductors. Therefore, we are able to see how these effects can remold and eventually suppress the gap. Furthermore, the semiclassical framework is able to cover the effect of a finite Ehrenfest time, which also causes the gap to shrink. However, for intermediate values this leads to the appearance of a second hard gap-a clear signature of the Ehrenfest time. [less ▲]

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See detailSemiclassical approach to the ac conductance of chaotic cavities
Petitjean, Cyril ULg; Waltner, Daniel; Kuipers, Jack et al

in PHYSICAL REVIEW B (2009), 80(11), 115310-12

We address frequency-dependent quantum transport through mesoscopic conductors in the semiclassical limit. By generalizing the trajectory-based semiclassical theory of dc quantum transport to the ac case ... [more ▼]

We address frequency-dependent quantum transport through mesoscopic conductors in the semiclassical limit. By generalizing the trajectory-based semiclassical theory of dc quantum transport to the ac case, we derive the average screened conductance as well as ac weak-localization corrections for chaotic conductors. Thereby we confirm respective random matrix results and generalize them by accounting for Ehrenfest time effects. We consider the case of a cavity connected through many leads to a macroscopic circuit which contains ac sources. In addition to the reservoir the cavity itself is capacitively coupled to a gate. By incorporating tunnel barriers between cavity and leads we obtain results for arbitrary tunnel rates. Finally, based on our findings we investigate the effect of dephasing on the charge relaxation resistance of a mesoscopic capacitor in the linear low-frequency regime. [less ▲]

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See detailCurie temperature, exchange integrals, and magneto-optical properties in off-stoichiometric bismuth iron garnet epitaxial films
Vertruyen, Bénédicte ULg; Cloots, Rudi ULg; Abell, J. S. et al

in Physical Review b (2008), 78(9), 094429

We have studied the influence of the stoichiometry on the structural, magnetic, and magneto-optical properties of bismuth iron garnet (Bi3Fe5O12) thin films grown by pulsed laser deposition. Films with ... [more ▼]

We have studied the influence of the stoichiometry on the structural, magnetic, and magneto-optical properties of bismuth iron garnet (Bi3Fe5O12) thin films grown by pulsed laser deposition. Films with different stoichiometries have been obtained by varying the Bi/Fe ratio of the target and the oxygen pressure during deposition. Stoichiometry variations influence the Curie temperature T-C by tuning the (Fe)-O-[Fe] geometry: TC increases when the lattice parameter decreases, contrary to what happens in the case of stoichiometric rare-earth iron garnets. The thermal variation of the magnetization, the Faraday rotation, and the Faraday ellipticity have been analyzed in the frame of the Neel two-sublattice magnetization model giving energies of -48 K (4.1 meV), -29 K (2.5 meV), and 84 K (7.3 meV) for the three magnetic exchange integrals j(aa), j(dd), and j(ad), respectively. Magneto-optical spectroscopy linked to compositional analysis by Rutherford backscattering spectroscopy shows that Bi and/or Fe deficiencies also affect the spectral variation (between 1.77 and 3.1 eV). Our results suggest that bismuth deficiency has an effect on the magneto-optical response of the tetrahedral Fe sublattice, whereas small iron deficiencies affect predominantly the magneto-optical response of the octahedral sublattice. [less ▲]

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See detailDephasing in quantum chaotic transport: A semiclassical approach
Whitney, Robert S.; Jacquod, Philippe; Petitjean, Cyril ULg

in PHYSICAL REVIEW B (2008), 77(4), 045315-22

We investigate the effect of dephasing (decoherence) on quantum transport through open chaotic ballistic conductors in the semiclassical limit of small Fermi wavelength to system size ratio, lambda(F)/L ... [more ▼]

We investigate the effect of dephasing (decoherence) on quantum transport through open chaotic ballistic conductors in the semiclassical limit of small Fermi wavelength to system size ratio, lambda(F)/L < 1. We use the trajectory-based semiclassical theory to study a two-terminal chaotic dot with decoherence originating from (i) an external closed quantum chaotic environment, (ii) a classical source of noise, and (iii) a voltage probe, i.e., an additional current-conserving terminal. We focus on the pure dephasing regime, where the coupling to the external source of dephasing is so weak that it does not induce energy relaxation. In addition to the universal algebraic suppression of weak localization, we find an exponential suppression of weak localization proportional to exp[-(tau) over tilde/tau(phi)], with the dephasing rate tau(-1)(phi). The parameter (tau) over tilde depends strongly on the source of dephasing. For a voltage probe, (tau) over tilde is of order the Ehrenfest time proportional to ln[L/lambda(F)]. In contrast, for a chaotic environment or a classical source of noise, it has the correlation length xi of the coupling or noise potential replacing the Fermi wavelength lambda(F). We explicitly show that the Fano factor for shot noise is unaffected by decoherence. We connect these results to earlier works on dephasing due to electron-electron interactions and numerically confirm our findings. [less ▲]

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See detailColossal positive magnetoresistance in a doped nearly magnetic semiconductor
Hu, Rongwei; Thomas, K. J.; Lee, Y. et al

in Physical Review B (2008), 77(8),

We report on a positive colossal magnetoresistance (MR) induced by metallization of FeSb2, a nearly magnetic or "Kondo" semiconductor with 3d ions. We discuss the contribution of orbital MR and quantum ... [more ▼]

We report on a positive colossal magnetoresistance (MR) induced by metallization of FeSb2, a nearly magnetic or "Kondo" semiconductor with 3d ions. We discuss the contribution of orbital MR and quantum interference to the enhanced magnetic field response of electrical resistivity. [less ▲]

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See detailFe-57 Mossbauer spectral and muon spin relaxation study of the magnetodynamics of monodispersed gamma-Fe2O3 nanoparticles
Rebbouh, Leila; Hermann, Raphaël ULg; Grandjean, Fernande ULg et al

in Physical Review b (2007), 76(17),

The Mossbauer spectra of monodispersed iron oxide nanoparticles with diameters of 4, 7, 9, and 11 nm have been measured between 4.2 and 315 K and fitted within the formalism for stochastic fluctuations of ... [more ▼]

The Mossbauer spectra of monodispersed iron oxide nanoparticles with diameters of 4, 7, 9, and 11 nm have been measured between 4.2 and 315 K and fitted within the formalism for stochastic fluctuations of the hyperfine Hamiltonian. In this model, the hyperfine field is assumed to relax between the six +/- x, +/- y, and +/- z directions in space with a distribution of relaxation rates that is temperature dependent. Muon spin relaxation measurements have been carried out on the 9 nm particles between 4.2 and 295 K. Both techniques reveal three regimes in the magnetic dynamics of these nanoparticles. In the low-temperature regime, between 4.2 and similar to 30 K, the nanoparticle magnetic moments are blocked and a spin-glass-like state is observed with nearly static hyperfine fields, as is indicated by the well resolved magnetic Mossbauer spectra and the slow exponential decay of the muon asymmetry functions. In the high-temperature regime, above similar to 125 K, the nanoparticle magnetic moments and, hence, the hyperfine fields, relax rapidly and a typical thermally activated superparamagnetic behavior is observed, as is indicated by the Mossbauer doublet line shape and the muon asymmetry functions that are unquestionably characteristic of monodispersed nanoparticles. In the intermediate regime between similar to 30 and 125 K, the Mossbauer spectra are the superposition of broad sextets and doublets and the muon asymmetry functions have been fitted with a sum of two terms, one relaxing term similar to that observed at and above 125 K and one term characteristic of static local fields. Hence, in this intermediate regime, the sample is magnetically inhomogeneous and composed of nanoparticles rapidly and slowly relaxing as a result of interparticle interactions. The magnetic anisotropy constants determined from both the Mossbauer spectral and magnetic susceptibility results decrease by a factor similar to 4 with increasing diameter from 4 to 22 nm and increase linearly with the percentage of iron(III) ions present at the surface of the nanoparticles. The interparticle interaction energy is estimated to be between 89 and 212 K from the temperature dependence of the magnetic hyperfine field measured on the 9 nm nanoparticles. [less ▲]

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See detailWeak ferromagnetism in Fe1-xCoxSb2
Hu, Rongwei; Hermann, Raphaël ULg; Grandjean, François-Xavier ULg et al

in Physical Review b (2007), 76(22),

Weak ferromagnetism in Fe1-xCoxSb2 is studied by magnetization and Mossbauer measurements. A small spontaneous magnetic moment of the order of similar to 10(-3)mu(B) appears along the b axis for 0.2 <= x ... [more ▼]

Weak ferromagnetism in Fe1-xCoxSb2 is studied by magnetization and Mossbauer measurements. A small spontaneous magnetic moment of the order of similar to 10(-3)mu(B) appears along the b axis for 0.2 <= x <= 0.4. Based on a structural analysis, we argue against extrinsic sources of weak ferromagnetism. We discuss our results in the framework of the nearly magnetic electronic structure of the parent compound FeSb2. [less ▲]

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See detailMagnetic and electronic properties of Eu4Sr4Ga16Ge30
Woods, G. T.; Marti; Beekman, M. et al

in Physical Review b (2006), 73(17),

Magnetization, static and ac magnetic susceptibility, nuclear forward scattering, and electrical resistivity measurements have been performed on polycrystalline Eu4Sr4Ga16Ge30, a type I clathrate that has ... [more ▼]

Magnetization, static and ac magnetic susceptibility, nuclear forward scattering, and electrical resistivity measurements have been performed on polycrystalline Eu4Sr4Ga16Ge30, a type I clathrate that has divalent strontium and europium ions encapsulated within a Ga-Ge framework. These data are compared with those of type I clathrates Eu8Ga16Ge30 and Eu6Sr2Ga16Ge30. The ferromagnetic ordering of these Eu-containing clathrates is substantially altered by the incorporation of strontium, as compared to Eu8Ga16Ge30. Ferromagnetism, accompanied by a relatively large negative magnetoresistance, is observed below 15 and 20 K in Eu4Sr4Ga16Ge30 and Eu6Sr2Ga16Ge30, respectively. An effective magnetic moment of 7.83 mu(B) per Eu ion is observed above 30 K for Eu4Sr4Ga16Ge30, a moment which is close to the free-ion moment of 7.94 mu(B) per europium(II) ion. [less ▲]

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See detailNeutron and nuclear inelastic scattering study of the Einstein oscillators in Ba-, Sr-, and Eu-filled germanium clathrates
Hermann, Raphaël ULg; Schweika, W.; Leupold, O. et al

in Physical Review b (2005), 72(17),

Inelastic neutron scattering measurements on Ba8Ga16Ge30 and Sr8Ga16Ge30 indicate the presence of soft local modes with Einstein oscillator energies of 4.9 +/- 0.1 and 4.4 +/- 0.1 meV, modes which are ... [more ▼]

Inelastic neutron scattering measurements on Ba8Ga16Ge30 and Sr8Ga16Ge30 indicate the presence of soft local modes with Einstein oscillator energies of 4.9 +/- 0.1 and 4.4 +/- 0.1 meV, modes which are associated with the lowest "rattling" mode of the Ba(B) and Sr(B) guests, respectively. Nuclear inelastic scattering measurements on Eu8Ga16Ge30 yield Einstein oscillator energies of between 3.0 +/- 0.3 and 7.5 +/- 1.2 meV for the different modes of the Eu guests. Further, the resonant character of the measurements on Eu8Ga16Ge30 reveals, without question, that neither of the Eu guests exhibit any vibrational modes above 9 meV. [less ▲]

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See detailStrongly decoupled europium and iron vibrational modes in filled skutterudites
Long, G. J.; Hermann, Raphaël ULg; Grandjean, Fernande ULg et al

in Physical Review b (2005), 71(14),

The europium partial vibrational density of states (DOS) in EuFe4Sb12 and the iron partial vibrational DOS in both EuFe4Sb12 and (CeFe4Sb12)-Fe-57 have been obtained by nuclear inelastic scattering. The ... [more ▼]

The europium partial vibrational density of states (DOS) in EuFe4Sb12 and the iron partial vibrational DOS in both EuFe4Sb12 and (CeFe4Sb12)-Fe-57 have been obtained by nuclear inelastic scattering. The results reveal the strong independence of the iron and rare-earth vibrational modes. The cage filling europium only participates significantly to the low-energy local vibrational modes. The force constants have been obtained from the measured probability of nuclear absorption. The energies of the peaks in the europium and iron DOS are in excellent agreement with the calculated DOS in LaFe4Sb12. The results indicate that nuclear inelastic scattering is the technique of choice for the study of the localized vibrational modes in thermoelectric "phonon glass" materials. [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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