A. Trzaskowska

High resolution Brillouin scattering studies of β-Gd2(MoO4)3; the bulk and surface phase transitions

We present here results of Brillouin scattering from bulk and surface phonons propagating in a well known ferroelectric–ferroelastic crystal β-Gd2(MoO4)3, in the temperature range covering the phase transition. Temperature dependences of the velocity of Rayleigh surface acoustic waves, propagating in a few planes of this crystal, have been calculated. The surface phonon velocities determined experimentally have been found to show a different character of temperature dependences, especially in the phase transition range.

Band gap in hypersonic surface phononic lattice of nickel pillars

Brillouin light scattering was applied for investigation of surface wave propagation in phononic materials made of a silicon surface loaded with a nanostructure of nickel pillars. The results revealed the presence of phononic energy gap in the GHz range. The presence of such an energy gap was theoretically confirmed by the finite element method. The width of the energy gap was found to be related to the height of the pillars and was shown to be limited by the frequencies of the modes localized in the pillars. The modes were thoroughly analysed.

Elasto-optical effect in composite crystal based on urea

Behaviour of bulk phonons propagating in clathrate compounds based on thiourea has been studied by Brillouin spectroscopy for different polarizations of incident and scattered beams. Elasto-optical coefficients p12, p13, p44 and p31 have been determined for host–guest type crystals. Pressure dependence of the intensity of excitations propagating in a structure of the host–guest type has been studied by the non-invasive method of Brillouin spectroscopy.

One-dimensional modulation of the stripe in a surface phononic lattice: The effect on propagation of surface waves

Brillouin light scattering was applied for the investigation of surface waves propagation in phononic materials made of a silicon substrate loaded with a permalloy layer and a modulated nanostructure of aluminum stripes. The results revealed the impact of one-dimensional modulation of the surface phononic crystal on the propagation of surface acoustic waves along the modulated aluminum stripes. The dispersion relation was experimentally and theoretically investigated. The new modes propagating in the investigated structure are localized in the stripes and are defined.

Pressure dependence of the elastic properties of composite host/guest type crystals

The elastic properties of host/guest type composite crystals, with urea as the host and an alkane as the guest, have been studied by Brillouin spectroscopy as a function of hydrostatic pressure. The effect of changing hydrostatic pressure in the range from 0 to 1400 bar on the propagation of acoustic phonons has been determined using three gases—helium, nitrogen and argon—as the pressure-exerting media.

Surface phonons in LiCsSO4 crystal studied by high-resolution Brillouin scattering

In crystals of lithium?caesium sulfate some anomalies in the behaviour of certain surface phonons have been detected by surface Brillouin scattering. The anomalies of the first type have been interpreted as being related to a change in crystal symmetry at a phase transition, while the second type of anomalies has been found to be related to surface phonon interactions with a soft bulk mode.

Elastic and Dielectric Behavior of Highly Disordered Pb(Sc1/2Ta1/2)O3 Single Crystal

The room temperature sound velocity v [111] = 4742 m/s and the elastic constant c[111] = (c11+2c12+4c44) = 203 GPa was determined from the Brillouin shift of the longitudinal acoustic mode in highly disordered Pb(Sc1/2Ta1/2)O3 single crystal. The degree of order S = 0.13 of the crystal was determined both from the occupation factor of the Sc and Ta atoms obtained for the full structure refinement at room temperature and 440 K from the ratios of the intensities of the superstructure and fundamental reflections. The dielectric response of the crystal is characterized by a dispersive maximum at Tε * max ≈ 250 K and the Vogel-Fulcher temperature TVF = 209 K.

Surface Phonons in LiCsSO4 Crystal

Results of the Brillouin scattering on the surface phonons propagating in ferroelastic crystal LiCsSO4 (LCS) in the temperature range covering its phase transition are presented. Surface acoustic phonons in different planes and at various depths from the surface have been studied.

Surface Phonons in Ferroelastic Crystals

Results of the surface phonon velocity V R measurements in three ferroelastic crystals {Gd 2 (MoO 4 ) 3 , LiCsSO 4 and Rb 4 LiH 3 (SO 4 ) 4 } over the temperature range covering their transitions are presented. No significant elastic softening was observed in the course of our studies. In a few cases an anomalous increase of V R at T C was observed. The observed behavior may be attributed to the properties of the surface layer, which in the case Brillouin scattering experiment, is penetrated to about 300 nm from the surface.

Tunable properties of spin waves in magnetoelastic heterostructure

Full ferroelastic and simultaneously ferroelectric materials are interesting candidates for applications in devices based on multiferroic heterostructures. They should allow for non-volatile and low-power writing of data bits in magnetoelectric random access memories. Moreover, ferroelasticity, in contrast to piezoelectric material, make magnetic information in ferromagnetic film resistant to external fields. As an example for such a system, we have studied the magnetoelastic interaction between a thin ferromagnetic layer of with a full ferroelastic–ferroelectric gadolinium molybdate crystal. We have investigated the influence of spontaneous strain onto magnetic properties of thin ferromagnetic film. Particularly, we have shown by Brillouin spectroscopy, that it is possible to modulate surface spin wave frequency of by spontaneous strain of gadolinium molybdate substrate.