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This paper reports on peculiar metamagnetic transitions which take place in antiferromagnetic, charge and orbitally ordered (AFCOO) manganites. At very low temperatures, the virgin magnetization curves of some of these compounds exhibit several, sharp steps giving rise to a staircase-like shape. This staircase effect is shown to be sensitive to various experimental parameters. Several potential interpretations of the staircase effect are discussed in relation to this set of results. A martensitic-like scenario, involving a leading role of the structural distortions associated to the collapse of the orbital ordering, is found to be the most plausible interpretation., To be published in J. Mag. Mag. Mat

The notion that stress can induce chronic tinnitus, or increase its intensity, is predominant in the literature on tinnitus. However, there is little empirical support for this claim, since previous studies rely merely on subjective reports. In the present study, we used an objective physiological measure of stress (i.e., basal secretion of the stress hormone cortisol), in order to assess the relationship between tinnitus and stress. We hypothesized that tinnitus, a permanent internal sound, should behave as a stressor and should be accompanied by chronically elevated cortisol levels in individuals with severe tinnitus. In addition, we hypothesized that suffering from severe tinnitus should generalize to an intolerance towards external sounds. Two groups each comprised of 18 participants (with and without tinnitus) matched on education and health status participated in the study. Tinnitus severity, as assessed by tinnitus-related distress, was high in half of the tinnitus participants, and low in the other half. Basal cortisol levels were measured using saliva samples (five saliva samples per day for 3 days within a week) taken in the participant's natural environment. Intolerance to external sounds was assessed psychometrically. The high tinnitus-related distress group had chronic cortisol levels greater than both the low tinnitus-related distress and control groups, and also displayed greater intolerance to external sounds. The low tinnitus-related distress and control groups did not differ from each other on either of these measures. Our study thus provides the first physiological and empirical evidence of a link between intolerance to both internal (tinnitus) and external sounds in persons with tinnitus, and is compatible with the clinical observation that severe tinnitus is associated with high stress levels.

The structure, resistivity, thermopower, and magnetic behaviors of two sets of samples ${\mathrm{CaMn}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{3}$ and ${\mathrm{CaMn}}_{1\ensuremath{-}y}{\mathrm{Mo}}_{y}{\mathrm{O}}_{3}$ $(0.04l~xl~0.08;$ $0.02l~yl~0.04)$ have been studied. All samples exhibit a magnetoresistance effect. The high-temperature region of all samples can be fitted well by a small polaron hopping model. The activation energy of Ru-doped samples decreases with doping while that of Mo-doped samples increases. However, for the same Mn valency, the Mo-doped system exhibits ferromagnetism in contrast to the Ru-doped ${\mathrm{CaMnO}}_{3}.$ The antiferromagnetic state of ${\mathrm{CaMn}}_{0.94}{\mathrm{Ru}}_{0.06}{\mathrm{O}}_{3}$ has been confirmed by neutron diffraction. This strongly suggests that the ${\mathrm{Ru}}^{5+}\ensuremath{-}\mathrm{O}\ensuremath{-}{\mathrm{Mn}}^{4+}$ antiferromagnetic superexchange for low doping levels prevails over ferromagnetic exchanges, i.e., ${\mathrm{Mn}}^{3+}\ensuremath{-}\mathrm{O}\ensuremath{-}{\mathrm{Mn}}^{4+}$ and ${\mathrm{Ru}}^{5+}\ensuremath{-}\mathrm{O}\ensuremath{-}{\mathrm{Mn}}^{3+}$ interactions. These electron-doped oxides exhibit large absolute values of thermopower at room temperature (Seebeck coefficient $|S|g100\ensuremath{\mu}{\mathrm{V}\mathrm{}\mathrm{K}}^{\ensuremath{-}1})$ accompanied by low values of their resistivity $(\ensuremath{\rho}l0.03\ensuremath{\Omega}\mathrm{cm})$ and thermal conductivity $(\ensuremath{\kappa}\ensuremath{\sim}5{\mathrm{W}\mathrm{}\mathrm{K}}^{\ensuremath{-}1}{\mathrm{m}}^{\ensuremath{-}1}).$ Therefore, they are good candidates for applications as n-type legs of thermopower generators to be used at high temperatures $(T\ensuremath{\gg}300\mathrm{K}).$

The antiferromagnetic, charge and orbitally ordered (AFCOO) ground state of some manganites like ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ can be efficiently destabilized by slight Mn-site substitutions. Such a weakened AFCOO state and related disorder effects were investigated in ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{Mn}}_{0.95}{\mathrm{Ga}}_{0.05}{\mathrm{O}}_{3}$ by combining specific-heat and magnetization measurements. The study was extended to the ferromagnetic state which can be installed in this compound by field application at low T. Under a large field, the temperature-driven collapse of this ferromagnetic state was found to be consistent with the Clausius-Clapeyron relation typical of first-order transitions. A comparative study of the various magnetoelectronic states encountered in the substituted and unsubstituted compounds was also carried out by investigating the low-temperature dependence of specific heat.

Field-induced magnetization jumps with similar characteristics are observed at low temperature for the intermetallic germanide Gd5Ge4and the mixed-valent manganite Pr0.6Ca0.4Mn0.96Ga0.04O3. We report that the field location -and even the existence- of these jumps depends critically on the magnetic field sweep rate used to record the data. It is proposed that, for both compounds, the martensitic character of their antiferromagnetic-to-ferromagnetic transitions is at the origin of the magnetization steps., Comment: 4 pages,4 figures

International audience; 2D misfit cobalt oxides combine a metallic behaviour at room temperature with a large thermopower, close to +90- +165μV/K depending on the composition. High temperature measurements have shown that these good properties persist up to 800K, which makes them interesting for high temperature applications as p-type legs. The results for the different misfit phases investigated will be presented. Other families of cobalt oxides with different kinds of structure, 1D or 2D, have been investigated in order to improve the figure of merit and to find n-type thermoelectric materials and some promising results will be shown. Also, measurements of manganese oxides at high temperature have been made to show their potentiality as n-type legs. © 2003 IEEE.

International audience; In the Ca-Co-O system, there exists at least two identified phases, Ca 3Co4O9 and Ca3Co2O 6 exhibiting 2D CoO2 planes and 1D Co-Co chains, respectively. Both oxides are characterized by large thermopower values at room temperature, the largest value being obtained for Ca3Co 2O6 (Seebeck coefficient, S300 K = 450 μV K-1). However, the electrical resistivity of the latter is too large (typically 50 Ω cm) for applications as thermopower materials. Interestingly, the substitutions of Ir4+ or Rh4+ for one cobalt out of two in the chain do not greatly affect the electronic properties in contrast to the substitution by Sc3+ (3d0). This emphasizes that the Ir or Rh cations can play a similar role to that of the Co cations. This opens a new route for the search of new thermoelectric materials alternative to the cobaltites. © 2003 Elsevier B.V. All rights reserved.

Substitutions at the Mn site of the charge-ordered ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ manganite is an effective way to induce abrupt jumps on the magnetic-field-driven magnetization curve. In order to get new insights into the origin of this remarkable feature, the ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{Mn}}_{0.97}{\mathrm{Ga}}_{0.03}{\mathrm{O}}_{3}$ perovskite manganite has been studied by neutron diffraction versus temperature and at 2.5 K in an applied magnetic field up to 6 T. A weak and complex antiferromagnetic order is found for the low-temperature ground state. Magnetic transitions, associated with structural ones, are evidenced for certain strengths of magnetic field, which gives rise to the steplike behavior corresponding to the magnetization curve. Small-angle neutron scattering provides evidence for a nucleation process of micron-size ferromagnetic domains which follows the magnetization behavior.

A round robin test aiming at measuring the high-temperature thermoelectric properties was carried out by a group of European (mainly French) laboratories (labs). Polycrystalline skutterudite Co0.97 Ni 0.03Sb3 was characterized by Seebeck coefficient (8 labs), electrical resistivity (9 labs), thermal diffusivity (6 labs), mass volume density (6 labs), and specific heat (6 labs) measurements. These data were statistically processed to determine the uncertainty on all these measured quantities as a function of temperature and combined to obtain an overall uncertainty on the thermal conductivity (product of thermal diffusivity by density and by specific heat) and on the thermoelectric figure of merit ZT. An increase with temperature of all these uncertainties is observed, in agreement with growing difficulties to measure these quantities when temperature increases. The uncertainties on the electrical resistivity and thermal diffusivity are most likely dominated by the uncertainty on the sample dimensions. The temperature-averaged (300–700 K) relative standard uncertainties at the confidence level of 68% amount to 6%, 8%, 11%, and 19% for the Seebeck coefficient, electrical resistivity, thermal conductivity, and figure of merit ZT, respectively. Thermal conductivity measurements appear as the least accurate. The moderate value of the temperature-averaged relative expanded (confidence level of 95%) uncertainty of 17% on the mean of ZT is essential in establishing Co0.97 Ni 0.03Sb3 as a high temperature standard n-type thermoelectric material.

In order to know if the origin of ferromagnetism induced by the substitution of Co or Ni for Mn in ${\mathrm{LaMnO}}_{3}$ could be due to their divalent oxidation states, a set of ${\mathrm{LaMn}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{O}}_{3}$ samples has been prepared for $xl~0.2$ and $M=\mathrm{Li},$ Zn, Ni, Co, Ga, and Rh. By combining resistivity, thermopower, magnetization, susceptibility measurements, and room-temperature structural refinements, we show that, similarly to Ni and Co, univalent $({\mathrm{Li}}^{+})$ and divalent $({\mathrm{Zn}}^{2+})$ $S=0$ cations induce both ferromagnetism and a more conductive behavior. In contrast, the $S=0$ trivalent cations $({\mathrm{Rh}}^{3+}$ and ${\mathrm{Ga}}^{3+})$ are found to preserve the orthorhombic ${O}^{\ensuremath{'}}$ structure, connected with the cooperative Jahn-Teller distortion of ${\mathrm{Mn}}^{3+}$ species in ${\mathrm{LaMnO}}_{3}.$ Accordingly, ${\mathrm{Rh}}^{3+}$- and-${\mathrm{Ga}}^{3+}$ substituted ${\mathrm{LaMnO}}_{3}$ manganites are only weak ferromagnets, and the resistivity increases in comparison to ${\mathrm{LaMnO}}_{3}.$ These results indicate that, for the investigated range of substitution (a maximum of 20%), both cobalt and nickel behave like divalent cations. The observation of ferromagnetism and the resistivity decrease, induced by univalent and divalent cations, ${\mathrm{Li}}^{+}$ and ${\mathrm{Zn}}^{2+},$ is due to the creation of ${\mathrm{Mn}}^{4+}$ species which favor ${\mathrm{Mn}}^{3+}/{\mathrm{Mn}}^{4+}$ double exchange.

We report a detailed study of step-like metamagnetic transitions in the magnetization and resistivity of polycrystalline Pr0.5Ca0.5Mn0.95Co0.05O3. The steps have a sudden onset below a critical temperature, are extremely sharp (width < 0.2 mT), and occur at critical fields which are linearly dependent on the absolute value of the cooling field in which the sample is prepared. Similar transitions are also observed at low temperature in non-Co doped manganites, including single crystal samples. These data show that the steps are an intrinsic property, qualitatively different from either previously observed higher temperature metamagnetic transitions in the manganites or metamagnetic transitions observed in other materials., 17pages,4 figures. accepted in Phy. Rev. Lett

The magnetic and transport properties of the manganites with the perovskite structure are mainly characterized by a competition between ferromagnetism and antiferromagnetism, and between a metallic like and an insulating behavior. Charge and orbital ordering, and phase separation play a prominent role in the appearance of such properties, since they can be modified in a spectacular manner by external factors, making the different physical properties metastable. There we describe two effects that deeply modify those properties, the doping of Mn sites and the thermal cycling under a magnetic field. The doping of Mn sites by various magnetic cations-Cr, Co, Ni, Ru, Rh, Ir-destroys charge/orbital-ordering and induces ferromagnetism and metallicity in the antiferromagnetic matrix of the manganites. The magnetic phase diagram of the systems Ln(1-x)Ca(x)MnO(3) is considerably modified by such doping. The metastability of the magnetic states is explained in terms of models based on the electronic structure of the doping elements in connection with a possible valence fluctuation. The thermal cycling is also a spectacular effect, observed in chromium doped manganites. For instance, an increase of resistivity by several orders of magnitude can be observed by thermal cycling under a magnetic field, whereas no effect is obtained in the corresponding undoped material. This behavior is interpreted in terms of strains induced charge localization, at the interface between ferromagnetic/antiferromagnetic domains in the antiferromagnetic matrix. (C) 2002 Elsevier Science Ltd. All rights reserved.

The magnetic, transport, and thermoelectric properties of a Tl-based misfit cobaltite have been investigated. Although this material exhibits a metallic behavior, the thermopower (Seebeck) is large, with room temperature values close to +90 \ensuremath{\mu} V/K. Compared to previously studied misfit cobalt oxides $[{\mathrm{Ca}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{9},(\mathrm{B}\mathrm{i},\mathrm{}\mathrm{P}\mathrm{b})\mathrm{S}\mathrm{r}\mathrm{C}\mathrm{o}\mathrm{O}]$ this Tl-based misfit is the only compound of this family which remains metallic and paramagnetic down to 2 K. On the one hand, this behavior emphasizes the importance of the edge-shared octahedra in the ${\mathrm{CoO}}_{2}$ layer for the thermoelectric properties of these materials. On the other hand, the absence of a magnetically ordered state at low temperature explains the absence of low temperature negative magnetoresistance. It gives support to a mechanism based on quantum fluctuations stabilizing the paramagnetic state rather than a magnetically ordered state.

The recognition of text and tune in songs was examined in a music-agnosic patient and five matched controls. Listeners had to focus on one component of the song at a time (text or music) and had to decide whether the component was familiar or unfamiliar. Songs were either matched (i.e., an original familiar or an original unfamiliar song) or mismatched (a combination of a familiar component with an unfamiliar one). Normal listeners displayed response patterns that are congruent with those obtained previously in different experimental settings and which showed that text and tune are difficult to separate. Data collected in the patient, however, suggest some independence between text and music in songs. Moreover, the usual asymmetry in favor of text was much reduced when later verses were used. Overall, the results are interpreted as revealing strong association, not integration, between the musical and the verbal component of familiar songs.

The possibility to induce ferromagnetism and insulator to metal transitions in small A site cation manganites Ln_{1-x}Ca_xMnO_3 by rhodium doping is shown for the first time. Colossal magnetoresistance (CMR) properties are evidenced for a large compositional range (0.35 \leq x < 0.60). The ability of rhodium to induce such properties is compared to the results obtained by chromium and ruthenium doping. Models are proposed to explain this behavior., 11 pages, 8 figures

Polycrystalline samples in the series Ti1-xTaxS2 with x varying from 0 to 1 were prepared using solid-liquid-vapor reaction and spark plasma sintering. Rietveld refinements of X-ray diffraction data are consistent with the existence of a full solid solution for x ≤ 0.4. Transport measurements reveal that tantalum can act as electron donor when substituted in the Ti sites. As a consequence, the electrical resistivity and the absolute value of the Seebeck coefficient decrease with Ta content due to an increase in the carrier concentration. The lattice thermal conductivity being reduced due to mass fluctuation effect, the ZT values in Ti0.95Ta0.05S2 is slightly increased as compared to TiS2.

Dense ceramics of the itinerant ferromagnet CoS2 have been prepared by the spark plasma sintering technique. The structural study confirms a cubic unit-cell for CoS2 with a = 5.539(6)angstrom (SG = Pa-(3) over bar). Scanning and transmission electron microscopy reveal the existence of sulfur deficient regions of composition "Co2S3" with a structure compatible to that of CoS2 where 0.5 S atom are missing in one out of two successive layers along the b direction. The volume of these regions estimated to be less than 1% is explained by possible S losses from the surface during the sintering. The physical properties measurements show a high T-C (122 K), large saturated magnetization (0.88 mu(B)/f.u.), with a similar to 100% magnetoresistance at 5K in 9 T. Also, the value of the residual resistivity ratio, rho(300K)/rho(5K) = 45, between those of crystal and conventional ceramics, attest for both good compacity and grain connectivity. Interestingly, the Seebeck coefficient exhibits negative values reaching S = -47.5 mu V K-1 at 675K and below T-C, S can be fitted by a diffusion model with a magnon term related to the ferromagnetism. A large power factor (S-2/rho) of 1mW m(-1) K-2 is obtained over a broad T range but the too high thermal conductivity (kappa(675 K) similar to 8.7W K-1 m(-1)) is a limiting physical parameter to use CoS2 ceramics in thermoelectric devices. (C) 2013 AIP Publishing LLC.

In this study, sensitivity to tonal relations was assessed by using real melodies instead of traditional scales or chords. Two groups of listeners-one trained, one untrained-rated the goodness of fit of each of the 12 tones of the chromatic scale as the final note of familiar and unfamiliar tune excerpts. The unfamiliar excerpts were the mirror forms in pitch and time of the familiar tunes. The results showed that musicians and nonmusicians exhibited responses that were governed by tonal relations with both familiar and unfamiliar tunes. These findings were corroborated by multiple-regression analysis, which revealed that the pattern of ratings reflected knowledge of the musical structure, beyond the contribution of surface features such as note frequency or pitch proximity between the two last tones.

Brain injury can drastically impair musical activities while sparing intellectual and linguistic abilities (see Marin 1982, and Basso 1993, for reviews). Conversely, musicianship can be maintained following brain insult that results in severe global cognitive decline (Beatty, Zavadil, Bailly and al. 1988). These facts suggest that musical abilities are specific functions that are subserved by a neural architecture dedicated to music processing (Peretz and Morais 1993; Sergent et al. 1992). Music is, however, not a monolithic entity. Examination of amusic patients leads to the fascinating realization that music cognition is not affected in its entirety, but in particular abilities only. The selective nature of some of these disorders will be the focus of the present paper. The central idea is that these deficits provide a rich source of information for the understanding of normal music cognition.

Magnetic properties of polycrystalline Sm0.1Ca0.9−yBayMnO3 (y=0.02, 0.06) samples have been investigated in the temperature range of 2–320 K, magnetic fields of up to 90 kOe, and under hydrostatic pressures of up to 12 kbar. It was found that the volume fraction of ferromagnetic (FM) phase at 5 K is about 27% for Sm0.1Ca0.88Ba0.02MnO3 and only ∼1% for Sm0.1Ca0.84Ba0.06MnO3. The compound Sm0.1Ca0.88Ba0.02MnO3 exhibits magnetic phase separation below TN≈TC≈99 K, which is consistent with a model of FM clusters embedded in antiferromagnetic (AFM) G-type matrix. For this sample, magnetization and ac susceptibility exhibit a cluster glasslike behavior below TC, while the resistivity exhibits pronounced thermal hysteresis around TC, indicating upon a plausible first order magnetic phase transition. For Sm0.1Ca0.84Ba0.06MnO3 two peaks observed in the temperature dependence of the ac susceptibility at low temperatures may be related to magnetic transitions, associated with the C- and G-AFM structures. Both, a sign...

To study magnetic correlations and spin dynamics of CaMn0.96Mo0.04O3 (CMMO) compound at paramagnetic (PM) state and to probe its low temperature magnetic ordering, X-band electron magnetic resonance (EMR) measurements were performed in 5K⩽T⩽600K interval. The model fittings of EPR peak-to-peak linewidth and double integrated intensity reveal an existence of antiferromagnetic (AFM) and ferromagnetic (FM) correlations at PM state. The enhancement of FM correlations upon cooling and its competition with AFM ones result in FM-like magnetic ground state of CMMO below 110K. The results of EMR measurements evidence that the low temperature magnetic ground state of CMMO may be better described by complex canted magnetic structure with net FM component than by the phase separated state.

Samples of the low-doped manganite La0.875Sr0.125?xCaxMnO3 (0?x?0.125) have been synthesized and the effect on the structural, magnetic and transport properties of decreasing the tolerance factor by replacing larger Sr2+ ions with smaller Ca2+ ions are reported. For samples with x?0.0625, a concentration (x) dependent structural transition (rhombohedral () to orthorhombic (Pnma)) has been detected at room temperature and the Curie temperature TC is found to decrease with increased Ca doping level. For samples with x?0.0625, a narrow metallic region exists and the corresponding insulator to metal transition temperature TMI decreases with increasing Ca content, i.e.?decreasing tolerance factor. In the paramagnetic region, x dependent crossover from Mott variable range hopping (Mott-VRH) to Shklovskii?Efros variable range hopping (SE-VRH) occurs as the Ca content increases. The thermoelectric power (TEP) of the samples increases substantially, varying inversely with the tolerance factor. These results are analysed from the consideration of increased bending of the Mn?O?Mn bond with the decrease of the average ionic radius of the A-site element and the tolerance factor t, which causes narrowing of the bandwidth, decrease of mobility of eg electrons and weakening of the double exchange (DE) interaction associated with the substitution of Ca.

After more than ten years of intensive studies on CMR manganites, the numerous results that have been obtained revealed an unpredicted richness of their chemistry and physics. In particular, the possibility to chemically tune the competition between the different ordering parameters linked to the degrees of freedom of spin, charge and lattice has allowed the creation of an infinite combination of compounds with remarkable properties. This point is illustrated by several examples based on half-doped compositions, i.e. for Mn3+/Mn4+ ratio close to 1, for which substitutions at the Mn site allow the amounts of antiferromagnetic charge ordered and ferromagnetic charge delocalized phases to be balanced. Special attention is paid to the induced abrupt magnetization jumps. Additionally, the compositions involving a majority of tetravalent manganese are also very attractive. Taking into account their lower amount of Jahn–Teller Mn3+ cations, different physics is observed, including metallicity close to CaMnO3 or robust charge/orbital ordered antiferromagnetic structures for sufficient amounts of trivalent manganese. A second section is devoted to these electron rich manganites.

Using thermoforging process, dense Ca3Co4O9 (Co349) thermoelectric oxides have been successfully textured. The various parameters influencing the formation of the Co349-textured material have been investigated. The electrical transport measurements show an anisotropy of the resistivity in good agreement with scanning electron microscopy observations. Texture is quantified by neutron-diffraction measurements and correlated to anisotropic resistivity measurements and Seebeck coefficients.

The search for new layered cobalt based oxides is very important to discover interesting physical properties as recently illustrated by the discovery of a large thermoelectric power in the metallic phase Na0.5CoO2 [1] and by the report on the superconductivity of the derived hydrated compound Na0.3CoO2,1.3H2O [2]. Recent investigations in the Sr-Co-M-O systems (M = Ga, Ti....) by means of transmission electron microscopy techniques have allowed to detect new layered cobaltites. Their structure has been obtained by combining high resolution images and powder X-ray/neutron diffraction data. Firstly, a new oxide, (Ga1/3Co2/3)2Sr2CoO6+δ, has been isolated [3]. Its complex structure is described from a modulation vector q* = q1a* + q2c*. For the as-prepared sample (δ≈0.4), it can be described in an orthorhombic supercell Bb2b (q1=1/3 and q2=1) with the unit cell parameters a=3ap√2, b=ap√2 and c=19.2034(4) A. The layer stacking consists in an intergrowth between a [SrCoO3] perovskite-type block and a block of triple [AO] layers, [(SrO)(Co2/3Ga1/3O1+δ/2)(Co2/3Ga1/3O1+δ/2)] in which several kinds of GaOx and CoOx polyhedra coexist. Low resistivities (ρ300K ≈ 10 Ω.cm) depending on the δ value have been measured whereas a positive thermoelectric power S300K = 30μV/K indicates the presence of holes (Co) in the CoO2 conducting layers. This value can be compared with those observed in the Na0.5CoO2 and the misfit [(A'-xCoy)n-2A2+x-yOn] [CoO2]b1/b2 (A'=Bi,Tl.. and A=Ca,Sr..) related cobaltites. Secondly, two hydrated oxyhydroxides have been prepared in air [4]. The structural study coupled to thermal analyses has shown that Sr3Co1.7Ti0.3O5(OH)2, xH2O and Sr4Co1.6Ti1.4O8(OH)2, xH2O are derived from the Ruddlesden-Popper n = 2 and n = 3 members, respectively. The T-dependence of the structure shows upon warming two broad structural transitions from hydrated oxyhydroxides to oxygen deficient RP structures via an anhydrous oxyhydroxide form. The phenomenon of water loss during warming up to 1000°C to obtain the parent RP structures is found to be reversible. The magnetic behavior of these phases is governed by the substituted amount of Ti (d) for cobalt species : cluster-glass and spin-glass like properties are observed for the hydrated n = 2 and n = 3 members, respectively.

The Bi–Sr–Co–O system has been investigated for small bismuth contents in order to study the formation of the misfit oxide series built up from the stacking of three rocksalt-type layers (n=3) with a single CdI2-type CoO2 hexagonal layer. Starting from nominal compositions, written as [Sr2Co1−xBixO3]RS[CoO2]1.8 (x=0.1, 0.2, 0.3, 0.4, and 0.5), samples have been synthesized and their structure has been analyzed by combining transmission electron microscopy techniques and powder x-ray diffraction data. For x≈0.5, intergrowths are clearly observed, made of a majority of triple (n=3) and a few quadruple (n=4) rocksalt-type layer-based misfit cobaltites. Transport measurements (2.5 up to 320 K) reveal that the Bi introduction reduces the resistivity, especially at room temperature. Furthermore, the thermopower (Seebeck coefficient S) of such intergrowth (S≈120μVK−1 at 300 K) is found to be of the same order as the one measured for the n=4 Bi–Sr cobaltite while the resistivity (ρ≈20mΩcm at 300 K) is significant...

Splayed configurations of columnar defects with different characteristic angles θi relative to the $$\vec c$$ have been achieved in single crystals of YBCO, (Tl,Bi)-1212 and Bi-2212. An increased pinning efficiency consistents with the splayed model of Hwa et al, has been observed with θi=10° for YBCO and (Tl,Bi)-1212. For the more anisotropic compound Bi-2212, higher angles up to θi=75° are necessary to obtain the same result, but these last results are more delicate to interpret.

Substitutions in the Mn-sublattice of antiferromagnetic, charge and orbitally ordered manganites was recently found to produce intriguing metamagnetic transitions, consisting of a succession of sharp magnetization steps separated by plateaus. The compounds exhibiting such features can be divided in two categories, depending on whether they are sensitive to thermal cycling effects or not. One compound of each category has been considered in the present study. The paper reports on the influence of two treatments: high-temperature annealing and grinding. It is shown that both of these treatments can drastically affect the phenomenon of magnetization steps. These results provide us with new information about the origin of these jumps in magnetization., accepted for publication in J.Appl.Phys

This series of experiments dealt with discrimination between two temporal patterns differing only by the insertion of an additional silent gap. In Experiment 1, patterns varied in metric and figural structure. Metric structure is described as the sense of temporal regularity that may occur between subjectively accented tones. Figural structure is described as the grouping of temporally adjacent tones separated by silences. Standard patterns were either strongly or weakly metric; comparison patterns differed from the standards by the insertion of a silence that disrupted either the metric structure alone or both the metric and the figural structures. Experiment 1 provided support for the roles of both metric and figural structures and provided support for the clock-induction model of Povel and Essens (1985) as an account of metric processing. In Experiments 2-4, discrimination of patterns with differing metric structures but identical figural structures was examined more closely. Rate of presentation of the patterns was varied. Multiple regression indicated that, independent of rate variations, discrimination improved as the absolute (not relative) duration of the silent gap increased. We argue that an additional timing mechanism, independent of pattern structure, is operative in temporal pattern discrimination. All the results were replicated across levels of music training of the listeners.

The thermoelectric properties of misfit cobaltites have been investigated. Their crystallographic structure consists in the stacking of layers of tilted CoO6 edge-shared octahedra, separated by rock-salt type layers. The Tl based family was first investigated : it is shown that by increasing the Tl content, the resistivity ρ can be reduced while keeping a large thermopower S. Another way to improve the figure of merit Z=S2/(ρκ) is to partially substitute Bi for Tl to increase S and keep a small ρ. A new family of Pb-based misfits has also been investigated. Two different techniques have been attempted to decrease ρ and/or increase S in this family : the partial substitution of Cu for Co, and the partial substitution of Ca for Sr.

The Seebeck coefficients of several ruthenates which structures derive from the perovskite, have been measured up to 800K. All the values above 300K are found to be in the range +25μV.K-1 to +35 μV.K-1, with a very weak dependence on both T absolute value and electrical resistivity. This demonstrates that S at high T depends mainly on the spin degeneracy term of the modified Heikes formula. The insensitivity of thermopower to the chemical doping confirms the applicability of the model. The present study also shows the good properties of ruthenates as thermoelectric p-type oxides for high T energy conversion.

This thesis deals with the synthesis, the structural study and the magnetic properties and electronic transport studies of different ruthenium oxide families, presenting various magnetic and electronic behaviors, with rutile, R-type hexaferrite and hollandite structures. The goal of this thesis was the study of the ruthenium oxide peculiarities probed by the Seebeck effect in the following materials: RuO2 rutile (edge-shared RuO6 chain interconnected by their vertices) with Boltzmann type transport dominated by electron-phonon interactions, BaCo2Ru4O11 et BaMn2Ru4O11 R-type hexaferrites (edge-shared RuO6 octahedra, forming kagome planes, and face-shared RuO6 octahedra) soft ferromagnetic bad metals, and two new hollandites Sr1.5Ru6.1Cr1.9O16 et Ba1.5Ru6.1Cr1.9O16 (double chains of edge-shared RuO6 octahedra, interconnected by their vertices) with localized transport and cluster-glass behavior. The synthesis of both new hollandites by solid state reaction allowed us to show the existence of negative magnetoresistance in this compound family. This thesis shows that the behavior of the Seebeck coefficient of ruthenium oxides with structures mainly consisting of edge-shared RuO6 octahedra presents two different behaviors. At low T, S strongly depends on the crystallographic structure and on the associated electronic structure. On the other hand, in the high T limit, S tends a common value independently of the structure as reported here for the R-type hexaferrites and the hollandites and as previously observed in the ferromagnetic metal SrRuO3 perovskite (apex-shared RuO6 octahedra) and in the metallic with Pauli-type magnetism quadruple perovskite LaCu3Ru4O12 (apex-shared RuO6 octahedra). In these R-type hexaferrites BaCo2Ru4O11 and BaMn2Ru4O11 and these two new hollandites Sr1.5Ru6.1Cr1.9O16 and Ba1.5Ru6.1Cr1.9O16, the high temperature Seebeck coefficient reaches a value dominated by the Ru spin entropy term., Dans son ensemble, cette thèse porte sur la synthèse, l’étude structurale et l’étude des propriétés magnétiques et de transport de différentes familles d’oxydes de ruthénium, présentant des comportements électroniques et magnétiques variés, de structure rutile, hexaferrite de type R et hollandite. Le but de ce travail était l’étude des particularités des oxydes de ruthénium sondées par l’effet Seebeck dans les matériaux suivants : RuO2 de structure rutile (chaînes d’octaèdres de RuO6 liés par leurs arêtes, interconnectées par leurs sommets) à transport de type Boltzmann dominé par les interactions électron-phonon, les hexaferrites de type R BaCo2Ru4O11 et BaMn2Ru4O11 (octaèdres de RuO6 liés par les arêtes, formant des plans kagomé, et octaèdres de RuO6 liés par une face) ferromagnétiques doux et mauvais métaux, et deux nouvelles hollandites Sr1.5Ru6.1Cr1.9O16 et Ba1.5Ru6.1Cr1.9O16 (doubles chaînes de RuO6 liés par les arêtes, interconnectées par les sommets) avec agglomérats de spins localisés. La synthèse de ces deux nouvelles hollandites par réaction à l’état solide a permis de mettre en évidence l’existence de magnétorésistance négative dans cette famille de composés. Cette thèse montre que le comportement du coefficient Seebeck S d'oxydes de ruthénium à structures constituées d'octaèdres RuO6 majoritairement liés par leurs arêtes présente deux comportements différents. À basse T, S dépend fortement de la structure cristallographique et de la structure électronique associée. Par contre, dans la limite haute T, S tend vers une valeur commune indépendamment de la structure comme rapporté ici pour les hexaferrites de type R et les hollandites, et comme observé précédemment dans la pérovskite SrRuO3 (octaèdres RuO6 liés par les sommets) ferromagnétique métallique et dans la quadruple pérovskite LaCu3Ru4O12 (octaèdres RuO6 liés par les sommets) métallique présentant un magnétisme de type Pauli. Dans ces hexaferrites de type R BaCo2Ru4O11 et BaMn2Ru4O11 et dans ces deux nouvelles hollandites Sr1.5Ru6.1Cr1.9O16 et Ba1.5Ru6.1Cr1.9O16, le coefficient Seebeck à haute température atteint une valeur dominée par l’entropie de spin du ruthénium.

The Measure of Gramaticality and Informativeness in natural discourse (MeGID) was designed to address the lack of tools specifically dedicated to measure language progression in connected speech in patients with aphasia. In the present pilot study, we wanted to examine the test-retest reliability and responsiveness to change of the MeGID.We showed promising results, in particular regarding the Informativeess score. This will have to be replicated in a study with more participants., La Mesure de la Grammaticalité et de l’Informativité du Discours (MeGID) est un test élaboré pour répondre au manque d’outils spécifiquement dédiés à l’évaluation de la progression langagière des patients aphasiques dans leur discours naturel. Nous avons réalisé l’étude pilote visant à tester la fidélité test-retest et la sensibilité au changement de la MeGID. De bons résultats ont été obtenus, notamment pour le score d’Informativité.Ceux-ci devront être confirmés dans une étude avec davantage de participants.

The relationship of the crystallographic, magnetic, and electronic structure have long been of highinterest in research. Strontium iron oxides have structural, charge, spin, and orbital degrees offreedom, and thus give rich information to study for the condensed matter scientists. In this thesis,we have systematically studied the strontium iron oxides based on the freedom of the iron charge:Fe3+ and Fe4+ mixed valence compound SrFeO2,75 , Fe3+ compound Sr3Fe2O6 and SrFeO2,5 with differentcoordination around Fe3+ and Fe2+ compound SrFeO2. The synthesis of the polycrystalline compoundsare through either solid state reaction or sol-gel method. Single crystals of SrFeO2,75 and SrFeO2,5have been prepared by floating zone furnace. The purity of all the compounds is checked by lab x-raydiffraction and Mössbauer spectroscopy. Electronic structures have been studied by x-ray absorptionspectroscopy for all these compounds. Special efforts have been used to investigate the magneticstructure of SrFeO2,75 and Sr3Fe2O6 ., Les diverses perovskites de strontium-fer présentent de très fortes corrélations entre la structurecristalline et les phénomènes d’ordre de lacunes d’oxygènes, de charge, de spin et d’orbitales. Danscette thèse, nous avons réalisé une étude systématique des relations entre les ordres de charges etles ordres de spins selon les différents environnements cristallographiques rencontrés pour lescations Fe3+ et Fe4+ dans la phase Sr4Fe4O11, pour le cation Fe3+ dans les phases Sr3Fe2O6 et Sr2Fe2O10et pour le cation Fe2+ dans la phase SrFeO2. Les synthèses des phases polycristallines furent réaliséesvia des voies « solide » ou « sol-gel » en complément de la synthèse de cristaux préparés à l’aide d’unfour à image à fusion de zone verticale pour les phases Sr4Fe4O11 et Sr2Fe2O10. La qualité cristalline etchimique des oxydes fut contrôlée par diffraction de rayons X sur poudre et spectroscopieMössbauer alors que l’étude de la structure électronique de chaque phase a été réalisée à l’aide despectroscopie d’absorption de rayons X. Finalement, les structures magnétiques des phases Sr3Fe2O6et Sr4Fe4O11 sont aussi présentées.

Conducting polymers (CPs) have recently gained the attention of the scientific community due to their prospective use in thermoelectric applications [1,2]. Particularly, it has been proven that an important parameter for tuning the thermoelectric properties and the charge transport behavior of the CP is the shape of the DOS in the band edge, where a more steep band edge would be translated in a semi-metallic behavior for the system, with higher thermoelectric efficiencies. In the present study the correlation between material structure, electronic structure and electronic/ thermoelectric properties, is investigated through careful material design, towards an efficient thermoelectric polymer material. Additionally, the hybrid devices were fabricated as an alternative means to further enhance the thermoelectric efficiency of the material., Les polymères conducteurs ont attiré l'attention de la communauté scientifique en raison de leur utilisation potentielle dans les applications thermoélectriques [1, 2]. En particulier, il a été prouvé qu'un paramètre important pour accorder les propriétés thermoélectriques et le comportement de transport de charge du polymères, est la forme du DOS dans le bord de bande. Dans la présente étude, la corrélation entre la structure du matériau, la structure électronique et les propriétés électroniques / thermoélectriques, est étudiée par une conception soigneuse et rigoureux du matériau, vers un matériau polymère, thermoélectrique efficace. En outre, les dispositifs hybrides ont été fabriqués comme un moyen alternatif pour améliorer encore l'efficacité thermoélectrique du matériau.