Ultrasonic attenuation determination of Hc1 and Hc2 for ErRh4B4 at 1.5 K

The attenuation coefficient of longitudinal sound waves propagating in ErRh₄B₄ has been measured as a function of applied magnetic field where the propagation direction (q) of the sound waves was oriented either parallel or perpendicular to H_applied. For both orientations there is evidence of a type II-1 superconducting transition at H_c1 for T ≈ 1.5 K. In addition, when q ⊥ H an increase in attenuation is evident at H_c2, which does not appear when q 6 H, consistent with theories developed by Tachiki et al. utilizing supercurrent screening of the internal magnetic fields.     

Ultrasonic attenuation in pure and Gd-Doped superconductors: LaSn3 and LaAl2

We have investigated the ultrasonic attenuation (UA) in the pure and magnetically doped superconductors LaSn₃ and LaAl₂, the latter being an ideal Abrikosov-Gorkov system. The UA of pure LaSn₃ and LaAl₂ agrees well with BCS prediction. The experiments in doped LaSn₃ proved difficult due to high background attenuation. The results in La_1?nGd_nAl₂ (_n = 0.377 at .%), though, show a significant discrepancy with the theories which is not understood.     

Dynamical scaling and ultrasonic attenuation in 4He near Tλ

Ultrasonic attenuation in ⁴He near T_λ has been measured at frequencies between 10.9 MHz and 163 MHz. The attenuation above T_λ is described by a scaling function as $\text{α∝ω}{}^{\mathrm{x}}\text{F(}\text{ε}\text{ω}{}^{\mathrm{Y}}\text{)}$, and which proves the dynamical scaling hypothesis.     

Anomalous ultrasonic attenuation and velocity change in LaAl2

The attenuation and velocity of longitudinal waves has been measured in superconducting and normal LaAl₂ in the frequency range from 15 to 225 MHz. Both in the superconducting and in the normal state an unusually large damping has been found superimposed on the relatively small attenuation due to the well known electron-phonon interaction. On cooling into the superconducting state the attenuation starts to drop only at temperatures well below T_c and — as in insulating glasses — it rises again below 0.8 K. In our view this indicates that two-level systems similar to the ones found in amorphous superconductors may be present in our crystalline LaAl₂ sample and are responsible for the observed acoustic anomalies.     

Structure and elastic properties of TeO2-BaF2 glasses

Binary tellurite (100−x)TeO₂-xBaF₂ glasses for different compositions of BaF₂ (x=8, 10, 12, 15, 18 and 20 wt%) have been prepared by rapid quenching method. The velocities and attenuation during the propagation of the ultrasonic waves in all glasses were measured using a transducer operated at a fundamental frequency of 5 MHz at room temperature. A progressive increase in BaF₂ content leads to a decrease in ultrasonic velocities and density, which is followed by an increase in attenuation. The existence of depolymerisation of Te co-ordination leads to the transformation of TeO₄ trigonal bipyramid units through TeO₃₊₁ polyhedron to TeO₃ trigonal pyramid units. This is responsible for the observed decrease in the measured and determined parameters with the addition of the modifier content.     

Anelastic effects in (AgI)x(Ag2O·B2O3)1−x superionic glasses

We present here the first measurements of acoustic absorption in (AgI)_x(Ag₂O·B₂O₃)_1?x superionic glasses at ultrasonic frequencies (5–45 MHz) and in the 80–434 K temperature range. The attenuation shows, at decreasing temperature, an unusually high peak which seems to be attributed to a thermally activated relaxation process. A possible microscopic explanation of this anomaly is proposed, in connection with the presence of mobile ions in those materials.     

Ultrasonic attenuation anomalies at the two transitions in antiferromagnetic FeGe2

The attenuation of longitudinal and shear sound waves is measured through the Néel temperature, T_N≈286 K, and the lower transition temperature, T_K≈265 K, of FeGe₂. Longitudinal sound with wavevector q along the [100] axis of this tetragonal antiferromagnetic metal shows an attenuation peak at T_N, which is reversibly suppressed by compressive uniaxial stress σ along [010]. The estimated pressure dependence of T_N is dT_N/dp=(?2.8±0.3) mK bar^?1. The peak at T_N shows thermal and stress hysteresis, which suggests that it is associated with domain wall motion and that this transition is first order.     

Sound propagation in the two dimensional magnetic system K2NiF4

We have measured the classic constants C₁₁, C₃₃, C₅₅ and C₆₆ in K₂NiF₄ as a function of temperature between 4.2 and 200 K. A small velocity and attenuation anomaly was observed in the C₁₁ mode at T_N = 97.2 K.     

Anomalies in the longitudinal ultrasonic attenuation and the velocity variation in the mixed state of a V3Si single crystal

In addition to sharp attenuation peaks of longitudinal sound waves propagating along the [001] axis of a V₃Si single crystal at the upper critical fields H_c2, new large attenuation and broad velocity peaks were observed in the mixed state. The new anomaly is explained by a mechanism related to the anisotropy of flux in the crystal tetragonally deformed by the band Jahn-Teller effect.     

Ultrasonic studies of attenuation and dispersion in NH4Br near the order-disorder transition

Velocity and attenuation of sound wave propagation along the [100] direction in NH₄Br were measured near its transition temperature T_c = 234.5 K at frequencies of 30–150 MHz. The experimental results for the high-frequency attenuation and the dispersive velocity shifts are found to be in good agreement with the model of a single critical relaxation time.     

Attenuation of longitudinal ultrasonic wave near the diffuse phase transition in CdF2

The attenuation of a longitudinal ultrasonic wave propagating in the [111] direction in CdF₂ is studied as function of temperature from 300K to 1030K. An ultrasonic attenuation peak has been observed for the first time near 983K. This peak is used to define the diffuse transition temperature (T_c = 983K) in CdF₂ which is well below its melting temperature of 1372K. The Arrhenius activation energy of anion motion above T_c was obtained from the temperature dependence of the attenuation and the theory of the dynamics of the coupled crystalline-cage-charged-liquid fluctuations. The elastic constant, $\text{C}{}_{11}\text{+2}\text{C}{}_{12}\text{+4}\text{C}{}_{44}\text{)}\text{3}$, measured simulataneously with the ultrasonic attenuation displays a large decrease near 983K in addition to the nearly linear decrease in the elastic constant with temperature.     

Oscillatory behaviour of ultrasonic attenuation in KH2PO4 near the phase transition temperature

Oscillations in ultrasonic attenuation have been observed in KH₂PO₄ near the ferroelectric phase transition temperature for longitudinal ultrasonic wave propagation along the polarization axis. Oscillations are present both above and below the transition temperature; the periods of oscillations are different in the two phases for the same ultrasonic frequency and the same ∣T ? T_c∣. The temperature dependence of the oscillations shows that they are due to the phase transition.     

Sub-millimeter third harmonic generation in n-InSb waveguide

Resonant third harmonic generation of a sub-millimeter wave in n-InSb waveguide embedded with a density ripple is investigated. The non-linearity arises through the modulation of free electron mass while the ripple accounts for the phase mismatch. The efficiency of the third harmonic generation is large. However, as the plasma frequency increases the attenuation rate of the third harmonic increases and the third harmonic efficiency decreases as (ω_pb/c) is raised.     

The structural properties of CdO-Bi2O3 borophosphate glass system containing Fe2O3 and its role in attenuating neutrons and gamma rays

A glass system with chemical formula xBi₂O₃-(30−x)CdO-10B₂O₃-20Fe₂O₃-40P₂O₅ (0≤x≤30) wt% is prepared to be used as radiation shield. The mass attenuation coefficient and half value layer of the glass system to gamma rays have been measured experimentally and compared with those determined from theoretical calculations using the mixture rule of WinXCom program. A database of effective mass removal cross-sections for fast neutrons is also introduced in this work. The obtained results of this study are correlated to the structural properties of these glasses obtained from their IR spectra and the influence of gamma and neutrons irradiation on these structural properties.     

Anomalous behavior of ultrasonic properties near 50 K in Rb0.30MoO3 and Rb0.30(Mo1−xVx)O3

Depending on the temperature, the charge density wave (CDW) nonlinear conductivity of the blue bronzes A_0.30MoO₃ (A=K, Rb) shows two different regimes: a strongly damped motion above ∼50 K and motion with almost no damping below ∼50 K. In a search for an elastic signature of this CDW behaviour, we performed ultrasonic measurements on Rb_0.30MoO₃ and Rb_0.30(Mo_1−xV_x)O₃ single crystals between 4 K and 300 K. In Rb_0.30MoO₃, at T∼50 K, upon cooling, a large increase of the sound velocity is observed. The ultrasonic attenuation coefficient shows an increase down to 50 K followed by a plateau. In Rb_0.30(Mo_1−xV_x)O₃ (x=0.4 at%) the anomaly broadens and is shifted towards higher temperatures. The results are discussed in terms of CDW glass.     

The crystal-field dependency of sound attenuation in the spin-3/2 ising model

The effects of crystal-field (D) on sound attenuation are considered for the spin-3/2 Ising model by using Onsager theory of irreversible thermodynamics. It is assumed that the sound wave couples to the order-parameter fluctuations, therefore, it decays mainly via order-parameter relaxation process. The order-parameters, magnetization and quadrupole moment, are defined in terms of exact recursion relations (ERR) on Bethe lattice (BL). After our analysis, two relaxation times are obtained and they are used to calculate the sound attenuation coefficient (α). Consequently, the critical behaviors of sound attenuation coefficient are investigated in terms of frequency (w) and Onsager coefficient (γ) for the coordination numbers q=3, 4 ad 6 near the second-order (T_c) and first-order (T_t) phase transition temperatures in the ferromagnetic phase regions for the negative and positive D values and the results are presented on the (k_BT/J, α) planes. It is found that the peaks about T_t’s are observed at the same temperature, but the peaks about T_c’s are observed shifted to lower and higher temperatures in increasing (w)’s and (γ)’s, respectively. In addition, the peaks are also obtained near the tricritical points for all q.     

A study of the 35Cl(p, γ)36Ar reaction and the energy levels of 36Ar

Proton energies and strengths of (p,γ) and (p, p₁) resonances of the ³⁵Cl + p reaction were determined for E_p = 0.4?3.0 MeV and 1.9?3.0 MeV, respectively. The γ-decay of 84 resonances was studied with a 40 cm³ Ge(Li) detector. The branching ratios and excitation energies of 38 bound levels were determined. A new bound level was observed at E_x = 8472.0 ± 1.0 keV. Doppler-shift attenuation experiments yielded lifetimes of 20 bound levels. Spins and/or parities for bound levels and resonances were derived on the basis of observed transition strengths.     

Total attenuation cross-sections of fluorescent X-rays of Zr,Sn, Ba,Au, Pb,Th and U in elements 6⩽Z⩽82

The total attenuation cross-sections in elements 6?Z?82 forK _α andK _β groups of lines of elements Zr, Sn and Ba andL _l ,L _α,L _β andL _γ groups of lines of the elements Au, Pb, Th and U have been measured. The experimentally measured attenuation cross-sections have been found in good agreement with the theoretical estimates.     

Ultrasonic attenuation of surface acoustic waves in a thin film of superconducting Nb3Sn

The attenuation of 660 MHz surface acoustic waves propagating in a thin film of Nb₃Sn 5000 Å thick has been measured as a function of temperature from 4.2 K to 16 K. The A 15 Nb₃Sn, electron-beam codeposited on YZ lithium niobate and annealed at 700°C, was studied using 5.1 μm wavelength interdigital electrodes. The film revealed a transition temperature of 14.2 ± 0.1 K and using the BCS theory, an energy gap 2Δ(0) = 3.5 k_BT_c.     

Optical and acoustic properties of 33PbIn1/2Nb1/2O3-35PbMg1/3Nb2/3O3-32PbTiO3 single crystals in an electric field

The influence of different conditions of applying a dc electric field (0 < E < 4 kV/cm) on the behavior of optical transmission and on the acoustic parameters (sound velocity and attenuation) in the [001]- and [011]-oriented single crystals 33Pb(In_1/2Nb_1/2)O₃-35PbMg_1/3Nb_2/3O₃-32PbTiO₃ existing near the morphotropic phase boundary has been investigated. It has been found that the optical transmission, sound velocity, and attenuation sharply change near the phase transition in a narrow range of electric fields for any method of their applying. In the field applied along [001], the change in the sound velocity due to the phase transition is 1.5 times greater than that in the field applied along [011]. This is caused by a larger contribution of the piezoelectric effect to the elastic modulus determining the sound velocity along [001] as compared to [011]. It has been shown that the number, symmetry, and stability of the phases formed in the field depend on the conditions of applying the field.