[en] The Raman spectra of CsSnCl₃ single crystals were recorded at various temperatures in the range of 77 to 300 K in a search for manifestation of any crystal phase transition. The vibrational modes are studied and the observation of Raman lines confirms that in the temperature range 85 to 296 CsSnCl₃ does not have the cubic perovskite structure

[en] Results of a Raman investigation on KCdBr₃ monocrystals are presented and compared with those obtained for other double halides as RbCdBr₃, KCdCl₃, and NH₄CdCl₃. The Raman spectra of KCdBr₃ recorded at 80 and 300 K were interpreted and found to be similar to that of NH₄CdCl₃ and other double halides. The similarity suggests that KCdBr₃ has the same structure as NH₄CdCl₃ - the orthorhombic space group of D_2h¹⁶ with four molecules per unit cell

[en] Pressure-induced amorphization is the subject of intense study for the past few years because of its importance in material science and in solid state physics. We reported a crystalline-amorphous phase transition at ca 60kbar in NaVO1/3, which is the lowest pressure for such transitions in ionic crystals. The transition is marked by the sudden appearance of very broad bands at the 800 and 350 cm/sup -1 regions. The amorphization includes the complete breaking up of the infinite chains of corner-linked tetrahedral VO/sub 4, most likely into VO/sup -/sub 3. On decompression, the amorphous phase transforms to another phase, probably also amorphous at ca 40 kbar. It reverts to the stable ambient condition α-phase upon heating. Here we report on the details of the transtitional region and the re-linking of the VO/sub 4 chains upon heating. (authors)

[en] Laser excitation studies of CaF₂ crystals doped with 0.01 to 10% Ho³⁺ using the second harmonic wavelength 532 nm of a pulsed Nd:YAG laser are carried out. Three fluorescence bands belonging to the ⁵F₄, ⁵S₂ → ⁵I₈, ⁵F₄, ⁵S₂ → ⁵I₇ and ⁵F₅ → ⁵I₈ transitions are detected. Fluorescence lifetimes of the first two transitions are measured and used for site-identification of new lines. Four upconverted fluorescence bands belonging to the ⁵F₃ → ⁵I₈, ⁵G₄ → ⁵I₈, ⁵G₅ → ⁵I₈, ⁵H₅, ⁵H₆ → ⁵I₈ transitions are also detected. A comparative study is made of two pairs of energy transfer mechanisms, which are multiphonon relaxation versus ion-pair relaxation and two-photon absorption versus ion-pair relaxation. The analysis of the concentration dependence of fluorescence intensities shows that ion-pair relaxation is the chief mechanism responsible for the fluorescence and upconversion behaviour of CaF₂:Ho³⁺. (orig.)

[en] Lithium metavanadate (LiVO₃) single crystals have been studied by Raman spectroscopy under high pressure up to 200 k-bar. Three phase transitions were observed and they are believed to be a series of transitions involving the breaking up of the infinite VO₄^- chains into VO₃^- ions of average symmetry C_3ν. On decompression, the LiVO₃ transforms into an amorphous phase instead of reverting to the ambient crystalline phase, similarly to what has been observed for α -NaVO₃. The difference in the behaviours between LiVO₃ and α -NaVO₃ on compression has been explained by the different sizes of the Li⁺ and Na⁺ ions. The restoration of the virgin crystalline phase and the relinking of the VO₄^- chains were observed after heating the reclaimed samples. (author)

[en] We report Brillouin light scattering data taken from an exchange spring bilayer, Co/CoPt. The results are analysed using a semi-classical model in the long wavelength limit, and we demonstrate how a measure of an anomalous volume anisotropy, which we tentatively ascribe to a magnetoelastic effect, can be obtained from frequency versus field measurements in this system

[en] Micro-Raman spectroscopy has been used to analyse the substrate temperature effects on high temperature superconducting YBa₂Cu₃O_7-x thin films grown by the in situ pulsed laser deposition method. In particular, the dependence of the epitaxy quality on substrate temperature T_s is studied. Our results reveal that films with the highest epitaxy degree are grown with substrate temperature T_s between 680 and 720 deg. C, in good agreement with previous superconducting transition temperature measurements and x-ray diffraction analyses. In addition, the formation and distribution of impurities produced during growth are identified by Raman spectra and Raman imaging, and they are found to be more pronounced at higher substrate temperatures. Finally, localized Raman analysis has been performed to investigate the orientation of the single crystal grains in films grown at substrate temperature T_s>760 deg. C. It is confirmed that, within the experimental error of 3 deg., the crystal a/b-axes of these single crystal grains have a strong tendency to orient themselves along the crystal axis of the substrate, independent of their size, shape and orientation of the domain boundaries. (author)

[en] The effects of laser irradiation on high-temperature superconducting YBa₂Cu₃O_7-x thin films have been investigated by micro-Raman spectroscopy. Laser heating affects YBa₂Cu₃O_7-x thin films to varying degrees at different laser power levels. For a laser power density below 1 mW μm^-2, laser irradiation causes only thermal expansion within the focused area. When the laser power density is increased to about 1.7 mW μm^-2, oxygen out-diffusion occurs. The orthorhombic to tetragonal structural phase transition was observed at 3.1 mW μm^-2. Above 4.3 mW μm^-2, chemical decomposition is inferred from the appearance of Raman bands due to the impurity phase BaCuO₂. Comparison between the laser-heated results and the furnace-heated results was made, and the role played by temperature gradient and stress in the laser-heated sample is discussed in detail. (author)

[en] Regular arrays of oval-shaped permalloy nanorings have been fabricated using deep ultraviolet lithography and their spin dynamics measured by Brillouin light scattering with the magnetic field applied along long (easy) axes of the rings. The dispersionless behavior of the spin wave modes observed reveals their standing wave nature. Two-dimensional simulations and analytical calculations have been performed for a single isolated nanoring. Results reveal that the observed modes can be interpreted in terms of quantized Damon-Eshbach modes due to lateral confinement in the finite size rings

[en] We have developed a theory of Brillouin light scattering (BLS) from spin wave excitations in non-collinear magnetisation structures. We compare the results of calculated spectra for scattering from the spiral state found in exchange-coupled hard/soft CoPt/Co bilayers during reversal with experimental data. Both the Stokes/anti-Stokes peak intensity ratio is described, as well as the asymmetry in peak frequency between the Stokes and anti-Stokes spectra. It is shown that the frequency asymmetry arises naturally in the presence of a spin spiral structure