Raman scattering from phonons and magnons in RFe3)BO3)4

Inelastic light scattering spectra of several members of the RFe3(BO3)4 family reveal a cascade of phase transitions as a function of temperature, starting with a structural, weakly first order, phase transition followed by two magnetic phase transitions. Those consist of the ordering of the Fe-spin sublattice revealed by all the compound, and a subsequent spin-reorientational transition for GdFe3(BO3)4. The Raman data evidence a strong coupling between the lattice and magnetic degrees of freedom in these borates. The Fe-sublattice ordering leads to a strong suppression of the low energy magnetic scattering, and a multiple peaked two-magnon scattering continuum is observed. Evidence for short-range correlations is found in the `paramagnetic' phase by the observation of a broad magnetic continuum in the Raman data, which persists up to surprisingly high temperatures.Comment: 17 pages, 13 figure

Data on vibrational spectra of the langasites Ln3CrGe3Be2O14 (Ln = La, Pr, Nd) and ab initio calculations

In “Lattice dynamics and structure of the new langasites Ln3CrGe3Be2O14 (Ln = La, Pr, Nd): vibrational spectra and ab initio calculations” [1], experimental and calculated results on lattice dynamics of the recently discovered new compounds La3CrGe3Be2O14, Pr3CrGe3Be2O14, and Nd3CrGe3Be2O14 are reported. These compounds belong to the langasite series and constitute a new class of low-dimensional antiferromagnets. The data presented in this article includes IR diffuse transmission spectra of powder samples of Ln3CrGe3Be2O14 (Ln = La, Pr, Nd) registered at room temperature with a Bruker 125HR Fourier spectrometer, Raman spectra taken in the backscattering geometry (also at room temperature) with a triple monochromator using the line 514, 5 nm of an argon laser as an excitation, results of the DFT calculations with the B3LYP and PBE0 hybrid functionals on the optimized crystal structures, eigenfrequencies and eigenvectors of the normal vibrational modes. These data can be used to analyse electron-phonon interaction and multiferroic properties of the new langasites and to compare the lattice dynamics of different langasites. The dataset is available on mendeley data public repository at https://doi.org/10.17632/32grbb4p82.1. © 2019 The Author(s)Russian Foundation for Basic Research, RFBR: 17-02-00603This work was supported by the Russian Foundation for Basic Research under Grant #17-02-00603 . Optical spectroscopy research was performed on the Unique Scientific Installation of the Institute of Spectroscopy “Multifunctional wide-range high-resolution spectroscopy” ( http://www.ckp-rf.ru/usu/508571 )

Lattice vibrations of alpha'-NaV2O5

We have measured far infrared reflectance and transmittance spectra as well as Raman scattering spectra of \alpha'-NaV2O5 single crystals for all the principal polarizations. The temperature range above the phase transition temperature T_c=35 K was investigated, mainly. On the basis of this experimental study and of the lattice dynamics calculations we conclude that the symmetry of NaV2O5 in the high temperature phase is described by the centrosymmetric D_{2h}^{13} space group. The assignment of the observed phonons is given. Values of dielectric constants are obtained from the infrared data. Asymmetric shapes of several infrared lines as well as higher order infrared vibrational spectra are discussed. The crystal field energy levels of the 3d electron localized at the V^{4+} site have been calculated in the framework of the exchange charge model using the values of effective charges obtained from the lattice dynamics calculations. According to the results of these calculations, the earlier observed broad optical bands in the region of 1 eV can be interpreted as phonon assisted d-d transitions.Comment: 12 pages, 8 figures, 5 tables; submitted to PR

Mechanical, microstructural and oxidation properties of reactively sputtered thin Cr-N coatings on steel

Thin (40 nm and 160 nm) CrN coatings were deposited on steel by reactive magnetron sputtering deposition, varying the N2 flow. The coatings were characterized in the as-deposited condition and after annealing in air at 500 °C for 1 h, by X-Ray Diffraction, Transmission Electron Microscopy, Raman and Fourier Transform Infrared spectroscopies. Hardness was measured by nanoindentation. Coatings have a nanocrystalline microstructure with the phase shifting from Cr2N to CrN, increasing grain size, thermal stability and resistance to oxidation with increasing N2. Also intrinsic coating hardness is influenced by both N2 flow during deposition and film thickness, as a result of changes in phase composition and microstructural properties

Structure and Crystallization Behavior of La2O3.3B2O3 Metaborate Glasses Doped with Nd3+ or Eu3+ ions

International audienceThe local structure and crystallization behavior of the stoichiometric La2O3.3B2O3 (LaMB) metaborate glass doped with Nd3+ or Eu3+ ions are studied using differential thermal analysis (DTA), X-ray diffraction (XRD), Raman scattering and 11B magic-angle spinning nuclear magnetic resonance (MAS NMR), optical absorbance and luminescence techniques. In the crystallized samples, XRD, NMR and Raman spectroscopy have detected the formation of only one crystalline phase (congruent crystallization of LaB3O6). No intermediate metastable crystalline phase has been detected before LaB3O6 crystals formation (single stage crystallization process). The observation of heat treated glass samples by scanning electron microscopy (SEM) and optical microscopy coupled with the study of the effect of varying the glass particle size on the DTA curves have both revealed that LaB3O6 crystallization only occurs by a heterogeneous nucleation mechanism (needle-shape crystals) from glass surface. The activation energy Ec of crystal growth has been determined by performing DTA experiments at different heating rates with the Kissinger (784 kJ/mol) and Ozawa (801 kJ/mol) equations than can be used for surface crystallization processes. The heterogeneous crystallization behavior and the spectroscopic results obtained in this work by comparing the LaMB glass with the LaB3O6 crystalline phase suggest the existence of significant structural differences between the amorphous and the crystalline phases contrary to what was previously reported in literature