CNRS Crystallography and Material Science Laboratory

Caen, France

CNRS Crystallography and Material Science Laboratory

Caen, France
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Kuchler R.,Max Planck Institute for Chemical Physics of Solids | Steinke L.,Max Planck Institute for Chemical Physics of Solids | Daou R.,Max Planck Institute for Chemical Physics of Solids | Daou R.,CNRS Crystallography and Material Science Laboratory | And 3 more authors.
Nature Materials | Year: 2014

Electron-like carriers in bismuth are described by the Dirac Hamiltonian, with a band mass becoming a thousandth of the bare electron mass along one crystalline axis. The existence of three anisotropic valleys offers electrons an additional degree of freedom, a subject of recent attention. Here, we map the Landau spectrum by angle-resolved magnetostriction, and quantify the carrier number in each valley: while the electron valleys keep identical spectra, they substantially differ in their density of states at the Fermi level. Thus, the electron fluid does not keep the rotational symmetry of the lattice at low temperature and high magnetic field, even in the absence of internal strain. This effect, reminiscent of the Coulomb pseudogap in localized electronic states, affects only electrons in the immediate vicinity of the Fermi level. It presents the most striking departure from the non-interacting picture of electrons in bulk bismuth. © 2014 Macmillan Publishers Limited.


Juillet O.,University of Caen Lower Normandy | Fresard R.,CNRS Crystallography and Material Science Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Intertwining of spin, charge, and pairing correlations in the repulsive two-dimensional Hubbard model is shown through unrestricted variational calculations, with projected wave functions free of symmetry breaking. A crossover from incommensurate antiferromagnetism to stripe order naturally emerges in the hole-doped region when increasing the on-site coupling. Although effective attractive pairing interactions are identified, they are strongly fragmented in several modes including d-wave pairing and more exotic channels related to an underlying stripe. We demonstrate that the entanglement of a mean-field wave function by symmetry restoration can largely account for interaction effects, and that our approach is exact for a two-site cluster. © 2013 American Physical Society.


Meher K.R.S.P.,CNRS Crystallography and Material Science Laboratory | Martin C.,CNRS Crystallography and Material Science Laboratory | Caignaert V.,CNRS Crystallography and Material Science Laboratory | Damay F.,CEA Saclay Nuclear Research Center | Maignan A.,CNRS Crystallography and Material Science Laboratory
Chemistry of Materials | Year: 2014

Oxides containing magnetic 3d transition metals offer a large family of structures with frustrated magnetic networks. Some of those incommensurate antiferromagnetic structures are responsible for the local breaking of inversion symmetry so that these oxides are called spin-induced ferroelectrics. As listed in the introduction of this short review, the number of these multiferroics continues to increase. As for applications, the coupling between these ferroisms is needed; some magnetic oxides, despite a lack of ferroelectric ground state, exhibit large magnetoelectric coupling with a magnetic-field-induced polarization. Thus, they are classified as "magnetoelectrics". In the present review, we focus on recently studied systems showing ferroelectric-like behaviors or large magnetoelectric coefficients. This will be illustrated by chromites with the comparison between ceramics of CuCrO2 and AgCrS2: they exhibit different antiferromagnetic ground states, centrosymmetric and noncentrosymmetric. For the magnetoelectrics, the example of the cobaltite, CaBaCo4O7, which is a polar ferrimagnet, is taken to illustrate the existence of large magnetoelectric coefficients in crystals. Then, the existence of spin-induced ferroelectricity in centrosymmetric orthochromites (RECrO3 with RE = Lu or Er) is discussed. Through this selection of potential multiferroics or magnetoelectrics, it is clear that many magnetic materials in different forms (bulk/crystal/thin film) remain to be studied. © 2013 American Chemical Society.


Guilmeau E.,CNRS Crystallography and Material Science Laboratory | Breard Y.,CNRS Crystallography and Material Science Laboratory | Maignan A.,CNRS Crystallography and Material Science Laboratory
Applied Physics Letters | Year: 2011

We report on the thermoelectric properties of CuxTiS2 bulk compounds. Copper cations have been intercalated into the layered chalcogenide TiS2 by spark plasma sintering. X-ray diffraction analysis coupled to transmission electron microscopy shows that the lattice constant c expands linearly as the Cu content x increases. The Cu-intercalation into TiS2 leads to substantial decrease in both electrical resistivity and lattice thermal conductivity as compared to those of pristine TiS2. The figure of merit, ZT, is increased up to 0.45 at 800 K for x 0.02. The power factor, PF, reaches 1.7 mW/mK2 in TiS2 at 325 K. © 2011 American Institute of Physics.


Singh K.,CNRS Crystallography and Material Science Laboratory | Maignan A.,CNRS Crystallography and Material Science Laboratory | Simon C.,CNRS Crystallography and Material Science Laboratory | Martin C.,CNRS Crystallography and Material Science Laboratory
Applied Physics Letters | Year: 2011

Dielectric permittivity (′) and electrical polarization (P) have been measured as a function of temperature for two polycrystalline ACr 2O4 spinels (A Fe and Co). Anomalies on the ′(T) curves are detected at the characteristic magnetic transition temperatures (TC, TS, and Tlock-in) for FeCr 2O4 and CoCr2O4 and also at the Jahn-Teller (JT) transition for FeCr2O4. The P(T) curves of both spinels exhibit transitions at TC showing that polar and ferrimagnetic states coexist in these oxides. The link between the distortion of the spinel structure due to the Jahn-Teller Fe2 and the larger polarization value at 8 K, P 35 C/m2, against P 3.5 C/m2 for CoCr2O4, is also discussed. © 2011 American Institute of Physics.


Noudem J.G.,CNRS Crystallography and Material Science Laboratory | Kenfaui D.,CNRS Crystallography and Material Science Laboratory | Chateigner D.,CNRS Crystallography and Material Science Laboratory | Gomina M.,CNRS Crystallography and Material Science Laboratory
Scripta Materialia | Year: 2012

A spark plasma sintering (SPS) device was modified to allow free deformation of grains perpendicular to the loading axis. The aim was to obtain lamellar thermoelectric Ca 3Co 4O 9 ceramics. The new process is referred to as edge-free spark plasma sintering or spark plasma texturing (SPT). SPT materials are compared to those processed by conventional sintering and traditional SPS in terms of microstructure, texture and high-temperature thermoelectric properties. The results highlight the decisive advantages of the SPT technique. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Sarkar T.,CNRS Crystallography and Material Science Laboratory | Pralong V.,CNRS Crystallography and Material Science Laboratory | Raveau B.,CNRS Crystallography and Material Science Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The dc magnetization and magnetic relaxation studies of the calcium-doped samples Y0.95Ca0.05BaCo2O5.5 and YBa0.95Ca0.05Co2O5.5 show the existence of a magnetic glasslike behavior in the family of cobaltites. Our investigations reveal glasslike arrest of kinetics at low temperature, which prevents the system from reaching its magnetic ground state. We show that the low-temperature state of these calcium-doped phases, which consists of coexisting antiferromagnetic and ferro- (or ferri-) magnetic phase fractions, can be tuned in a number of ways. Our observations establish that the low-temperature state of this oxide is not in thermal equilibrium. The glassy state is formed with the assistance of an external magnetic field, which makes it distinctly different from the more well-known metastable state, the spin-glass state. The cooling field can tune the fractions of the coexisting phases, and the glasslike state formed at low temperature can also be devitrified by warming the sample. The role of Ca doping in the appearance of these phenomena is discussed in terms of phase separation, involving Co3 + disproportionation into Co4+ ferromagnetic clusters and Co2+ antiferromagnetic clusters. © 2011 American Physical Society.


Raveau B.,CNRS Crystallography and Material Science Laboratory
Angewandte Chemie - International Edition | Year: 2013

Transition-metal oxides have been widely studied for understanding the physics of strongly electron-correlated systems. The crucial role of crystal chemistry for the discovery of three families: the high Tc superconducting cuprates, the colossal magnetoresistance manganates, the thermoelectric, and multiferroic cobaltates, is explored. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Gascoin F.,CNRS Crystallography and Material Science Laboratory | Maignan A.,CNRS Crystallography and Material Science Laboratory
Chemistry of Materials | Year: 2011

The features of potentially efficient thermoelectric material, AgCrSe 2, exhibiting high Seebeck coefficient, relatively high electrical resistivity, but ultralow thermal conductivity comparable to that of a glass are presented. AgCrSe2 has electrical resistivity ranging in the tenths of milliω· cm. The layered compound AgCrSe2 is a known Ag-ion conductor whose structure can be described as CdI2-type layers of CrSe2- in which the Cr3+ cations are in a distorted octahedral coordination by Se2- anions. There are two different tetrahedral sites in the structure of AgCrSe2 situated between the CrSe2- sandwiches that form a slightly puckered honeycomb lattice. The disorder created by the mixed occupation of the cationic site by the calcium and the ytterbium deteriorates the thermal conduction that becomes temperature independent.


Raveau B.,CNRS Crystallography and Material Science Laboratory
Comptes Rendus Chimie | Year: 2011

Transition metal oxides represent a vast field for the study of strongly correlated electron systems, at the interface of crystal chemistry and physics. We describe herein the factors which govern the magnetic and transport properties of several families of oxides, which are promising functional materials: high TC superconductive cuprates, colossal magnetoresistance (CMR) manganites, thermoelectric cobaltites and multiferroic perovskites. © 2011 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.

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