F. Ganot

Brillouin scattering from the icosahedral quasicrystal Al70.4Mn8.4Pd21.2

Abstract We report on acoustic surface waves in quasicrystal Al 70.4 Mn 8.4 Pd 21.2 studied using Brillouin spectroscopy. Our data are fitted with a spectral density modelization and our results are compared to those obtained from previous inelastic neutron scattering and ultrasonic propagation measurements on the bulk samples Al 68.7 Mn 9.6 Pd 21.7 .

Mechanical characterizations of diamond carbon films made by PACVD

b ´´ ´ Abstract Mechanical and surface properties associated with their wettability were investigated for diamond films deposited on titanium alloy by a two-step microwave PACVD process at 600 8C. Polycrystalline and smooth fine grained diamond films were investigated. The elastic properties of the diamond layers were studied by Brillouin light scattering spectroscopy in order to determine their evolution as a function of the diamond purity. The effective elastic properties of these films with hexagonal effective symmetry were determined. The elastic constants decrease when diamond purity is lowered. The wettability tests can lead to the determination of superficial energy. A strong correlation is noticed between the wettability and superficial energy with the content of sp . 2002 Elsevier Science B.V. All rights reserved. 2

Ultrasonic propagation and Brillouin scattering studies in the 1D-ferromagnet CsNiF3

The elastic constants of the ID-ferromagnet CsNiF3 and their temperature dependence in the 10 K – 300 K range have been obtained using Brillouin scattering and ultrasonic propagation measurements. The results show a marked anisotropy. A small softening of C44 is observed when T decreases : it could arise from magnetic correlations. Comparison with previous experimental data derived from other techniques is discussed.

Brillouin scattering investigation of the low temperature phase transition in K2ZnCl4 and Rb2ZnCl4

Abstract In K2ZnCl4 and Rb2ZnCl4, Brillouin scattering of longitudinal acoustic phonons (C11, C22, C33) is performed as a function of temperature around the low temperature structural phase transition at To. Small and different anomalies are observed in both materials. These anomalies are compared to those observed at T3 in Rb2ZnBr4 by Horikx et al. 9 and are tentatively related to the mechanism of the transition.

Brillouin study of phonons, magnons and magnetoelastic coupling in the antiferromagnet KNiF3

Brillouin scattering by magnons and acoustic phonons in KNiF3 has been studied as function of the temperature. At low temperature, we observe unusually large splittings of the phonon Brillouin lines, related to the multidomains structure of the samples. Using our determination of the anisotropy constant, K = 1.1×104 erg/cm3, we calculate from the splitting of the longitudinal [1, 1, 0] phonon a magnetoelastic coefficient ‖b2‖ = 3.3×107 erg/cm3. We also study the domains reorientation under an applied magnetic field.

Brillouin scattering in ultrathin permalloy films: monolayers and multilayers with alumina interfaces

Abstract We present a Brillouin scattering study of single and multilayers thin (1,1,1) textured films of Permalloy with amorphous alumina interfaces prepared by rf sputtering [1]. From the spin wave spectra we can determine the gyromagnetic factor and the total anisotropy field. The results are in agreement with FMR experiments performed on the same samples [1]. We confirm the existence of a rather large surface anisotropy ( K s = 0.35 erg cm −2 ). The surface elastic wave spectra are also analysed: the deduced effective shear stiffness constant C 44 of Permalloy agrees with theoretical predictions.

Phase transitions in tetrafluoroaluminates RbAlF4 and KAlF4: brillouin scattering and ultrasonic propagation

Abstract RbAlF4 and KAIF4 belong to the family MAIF4 (M = K, Rb, Tl) of layered tetrafluoraluminates undergoing several phase transitions starting from a real or virtual high-temperature tetragonal aristotype structure (phase I-P4/mmm, Z = 1) characterized by a two-dimensional arrangement of AlF6 octahedra in sheets separated by K+ or Rb+ cations. The main feature of both compounds is the dominant role of the rotations of the AlF6 octahedra related to softenings of normal modes which are involved in the mechanisms of the successively encountered structural transformations (Bulou and Nouet, 1982; Bulou, 1985). These transformations can be interpreted in the framework of a Landau model, taking into account the pertinent order parameters associated with the soft modes at appropriate values of the wave-vector and including in addition their coupling with the strains: this leads to predictions of the elastic behaviour in the vicinity of the phase transitions studied by measuring the temperature dependence of t...

Phase transitions in K1-xRbxAlF4: II - brillouin and ultrasonic studies

Abstract The concentration dependence of the phase transitions features has been studied in K1-xRbxAlF4 for x varying between 0 and 0.09 through Brillouin and ultrasonic measurements. For x larger than 0.02, a new phase (IIIa) appears in the sequence phase II-phase IV of pure KAlF4. The elastic constants show pretransitional and transitional anomalies around the II-IIIa first order transition at T0(x) which are supported by a Landau development of the free energy up to the 6th order using the appropriate order parameter (X3 symmetry soft mode) adequately coupled to the strains, where only the second order term varies with x and is written as α(T-Tc(x)). This model also agrees with birefringence measurements (see paper III).

Brillouin scattering and ultrasonic investigations in the 1D-ferromagnet CsNiF3

Abstract The elastic constants of CsNiF 3 are derived versus temperature from Brillouin spectroscopy (5–300 K) and ultrasonic propagation (100–300 K). The results show a marked anisotropic elastic behaviour. A softening of C 44 below 170 K could arise from magnetic correlations. No effect of magnetic field is observed upon the longitudinal modes.

Brillouin scattering in Co/Cu/Co and Co/Au/Co trilayers: anisotropy fields and interlayer magnetic exchange

Abstract Magnetic anisotropy and interlayer exchange have been studied by Brillouin scattering on textured sandwiched Co/Cu/Co or Co/Au/Co structures normal to a 〈111〉 (pseudo-fcc) axis or to a 〈0001〉 (pseudo-hcp) axis, obtained by ultrahigh-vacuum evaporation on oxidized silicon or on float glass substrates. The surface contribution to the uniaxial anisotropy is approximately constant in all magnetic layers ( K s ≈ 0.8 erg cm −2 ). The volume contribution is strongly sample dependent. In Co/Au/Co, an oscillatory variation of the interlayer exchange is observed with a pseudo-period of 4.1 monolayers and a damping length of 5.1 monolayers, in good agreement with previously published determinations.