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Search Results: 1 - 10 of 461647 matches for " A. Revcolevschi "
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High frequency magneto-electrodynamics of La_(1-x)Sr_xMnO3 single crystals
H. Srikanth,B. Revcolevschi,S. Sridhar,L. Pinsard,A. Revcolevschi
Physics , 1997,
Abstract: The radio frequency (RF) response of La1-xSrxMnO3 single crystals reveal a variety of features associated with the structural, electronic and magnetic properties of the system. The resonance technique operating at ~ 4 MHz employed in this study is sensitive to small changes in both the magnetic susceptibility and resistivity of the samples. Very sharp changes in frequency are observed at the ferromagnetic (FM) and structural phase transitions in both the metallic (x = 0.175) and insulating (0.125) crystals studied. In addition to the known transitions identified as FM and orthorhombic distortions, our experiments show rich structures which are not observed in conventional DC magnetization and transport experiments. Our results demonstrate that RF experiments are ideally suited to investigate the complex phase diagram in the manganites. The colossal frequency change that we observe at the FM transition in the La1-xSrxMnO3 crystals is indicative of the enormous potential for using these materials in high frequency switching applications.
X-ray Investigation of the Magneto-elastic Instability of alpha'-NaV2O5
S. Ravy,J. Jegoudez,A. Revcolevschi
Physics , 1998, DOI: 10.1103/PhysRevB.59.R681
Abstract: We present an X-ray diffuse scattering study of the pretransitional structural fluctuations of the magneto-elastic transition in alpha'-NaV2O5. This transition is characterized by the appearance below Tsp~35K of satellite reflections at the reduced wave vector (1/2,1/2,1/4). A large regime of structural fluctuations is measured up to 90 K. These fluctuations are three dimensional between Tsp and ~50K and quasi-one dimensional above ~60K. At 40 K the anisotropy ratio is found to be (xib :xia :xic)= (3.8 : 1.8 : 1), which reveals the importance of transverse interactions in the stabilization of the low temperature phase. We discuss our results within the framework of recent theories dealing with the simultaneous occurrence of a charge ordering, a spin gap and a lattice distortion in this intriguing compound.
Universal behavior of spin-mediated energy transport in S=1/2 chain cuprates: BaCu2Si2O7 as an example
A. V. Sologubenko,H. R. Ott,G. Dhalenne,A. Revcolevschi
Physics , 2003, DOI: 10.1209/epl/i2003-00384-1
Abstract: The thermal conductivity of the spin-1/2 chain cuprate BaCu2Si2O7 was measured along different crystallographic directions in the temperature region between 0.5 and 300 K. The thermal conductivity along the chain direction considerably exceeds that along perpendicular directions. Near the antiferromagnetic transition at T_N = 9.2 K the data indicates enhanced scattering of phonons by critical fluctuations in the spin system. A comparison of the data above T_N with available results on similar materials reveals similarities in the main features of the temperature dependence of the mean free path of itinerant spin excitations. This universal behavior is most likely caused by the spin-lattice interaction.
Multiple spin-flop phase diagram of BaCu2Si2O7
V. N. Glazkov,G. Dhalenne,A. Revcolevschi,A. Zheludev
Physics , 2010, DOI: 10.1088/0953-8984/23/8/086003
Abstract: The quasi one-dimensional compound BaCu2Si2O7 demonstrates numerous spin-reorientation transitions both for a magnetic field applied along the easy axis of magnetization, and for a magnetic field applied perpendicular to it. The magnetic phase diagram for all three principal orientations is obtained by magnetization and specific heat measurements. Values of all critical fields and low-temperature values of magnetization jumps are determined for all transitions.
Optical spectroscopy of pure and doped CuGeO3
A. Damascelli,D. van der Marel,G. Dhalenne,A. Revcolevschi
Physics , 1999, DOI: 10.1103/PhysRevB.61.12063
Abstract: We investigated in detail the optical properties of several Cu(1-delta)Mg(delta)GeO3 (with delta=0,0.01), and CuGe(1-x)B(x)O3 with B=Si (x=0,0.007,0.05,0.1), and Al (x=0,0.01) single crystals, in the frequency range 20-32000 cm^-1. We report temperature dependent reflectivity and transmission measurements, performed with polarized light in order to probe the anisotropy of the crystals along the b and c axes, and optical conductivity spectra obtained by Kramers-Kronig transformation or direct inversion of the Fresnel formula. Special emphasis is given to the far-infrared phonon spectra. The temperature dependence of the phonon parameters is presented and discussed in relation to the soft mode issue in CuGeO3. For T
Magnetic resonance study of the spin-reorientation transitions in the quasi-one-dimensional antiferromagnet BaCu2Si2O7
V. N. Glazkov,A. I. Smirnov,A. Revcolevschi,G. Dhalenne
Physics , 2005, DOI: 10.1103/PhysRevB.72.104401
Abstract: A quasi-one dimensional antiferromagnet with a strong reduction of the ordered spin component, BaCu2Si2O7, is studied by the magnetic resonance technique in a wide field and frequency range. Besides of conventional spin-flop transition at the magnetic field parallel to the easy axis of spin ordering, magnetic resonance spectra indicate additional spin-reorientation transitions in all three principal orientations of magnetic field. At these additional transitions the spins rotate in the plane perpendicular to the magnetic field keeping the mutual arrangement of ordered spin components. The observed magnetic resonance spectra and spin-reorientation phase transitions are quantitatively described by a model including the anisotropy of transverse susceptibility with respect to the order parameter orientation. The anisotropy of the transverse susceptibility and the strong reduction of the anisotropy energy due to the quantum spin fluctuations are proposed to be the reason of the spin reorientations which are observed.
Infrared study of spin-Peierls compound alpha'-NaV2O5
D. Smirnov,J. Leotin,P. Millet,J. Jegoudez,A. Revcolevschi
Physics , 1998, DOI: 10.1016/S0921-4526(98)00633-4
Abstract: Infrared reflectance of alpha'-NaV2O5 single crystals in the frequency range from 50 cm-1 to 10000 cm-1 was studied for a, b and c-polarisations. In addition to phonon modes identification, for the a-polarised spectrum a broad continuum absorption in the range of 1D magnetic excitation energies was found. The strong near-IR absorption band at 0.8 eV shows a strong anisotropy with vanishing intensity in c-polarisation. Activation of new phonons due to the lattice dimerisation were detected below 35K as well as pretransitional structural fluctuations up to 65K.
The metal-insulator transition of the ferromagnetic La7/8Sr1/8MnO3 probed by spin waves: a 2D stripe superstructure
M. Hennion,F. Moussa,P. Lehouelleur,P. Reutler,A. Revcolevschi
Physics , 2006,
Abstract: We report a study of spin waves in hole-doped ferromagnetic La7/8Sr1/8MnO3, in the metallic state (165K) below TC (181K) and through the puzzling metal-insulator transition which occurs at TO'O''=159K. They reveal very unusual excitations. Propagating spin waves are observed in the small q-range up to q=0.25 (lambda=4a), and, beyond, four dispersionless levels. Both types of excitations have a quasi two-dimensional (2D) character. The transition is revealed by a folding of the dispersed magnon branch at q=1/8. In the metallic state, the dispersionless levels reveal ferromagnetic domains with 4 lattice spacings for their size along a and b. They lead to a picture of charge segregation with hole-poor domains surrounded with hole-rich paths. Within this description, the transition appears as the ordering of domains, which can be interpreted in terms of a 2D superstructure of orthogonal stripes.
Phonon thermal conductivity in doped $\rm\bf La_2CuO_4$: Relevant scattering mechanisms
C. Hess,B. Büchner,U. Ammerahl,A. Revcolevschi
Physics , 2003, DOI: 10.1103/PhysRevB.68.184517
Abstract: Results of in-plane and out-of-plane thermal conductivity measurements on $\rm La_{1.8-x}Eu_{0.2}Sr_xCuO_4$ ($0\leq x\leq0.2$) single crystals are presented. The most characteristic features of the temperature dependence are a pronounced phonon peak at low temperatures and a steplike anomaly at $T_{LT}$, i.e., at the transition to the low temperature tetragonal phase (LTT-phase), which gradually decrease with increasing Sr-content. Comparison of these findings with the thermal conductivity of $\rm La_{2-x}Sr_xCuO_4$ and $\rm La_2NiO_4$ clearly reveals that in $\rm La_{2-x}Sr_xCuO_4$ the most effective mechanism for phonon scattering is impurity-scattering (dopants), as well as scattering by soft phonons that are associated with the lattice instability in the low temperature orthorhombic phase (LTO-phase). There is no evidence that stripe correlations play a major role in suppressing the phonon peak in the thermal conductivity of $\rm La_{2-x}Sr_xCuO_4$.
Heat transport by lattice and spin excitations in the spin chain compounds SrCuO_2 and Sr_2CuO_3
A. V. Sologubenko,K. Gianno,H. R. Ott,A. Vietkine,A. Revcolevschi
Physics , 2001, DOI: 10.1103/PhysRevB.64.054412
Abstract: We present the results of measurements of the thermal conductivity of the quasi one-dimensional spin S=1/2 chain compound SrCuO_2 in the temperature range between 0.4 and 300 K along the directions parallel and perpendicular to the chains. An anomalously enhanced thermal conductivity is observed along the chains. The analysis of the present data and a comparison with analogous recent results for Sr_2CuO_3 and other similar materials demonstrates that this behavior is generic for cuprates with copper-oxygen chains and strong intrachain interactions. The observed anomalies are attributed to the one-dimensional energy transport by spin excitations (spinons), limited by the interaction between spin and lattice excitations. The energy transport along the spin chains has a non-diffusive character, in agreement with theoretical predictions for integrable models.
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