Ultrasonic attenuation of aluminium in transverse magnetic field

The attenuation of longitudinal sound wave in Al single crystal in high transverse magnetic field has been calculated by 4-OPW approximation. The wave vector of the sound wave is parallel to [1$\text{1}$0] axis. In general, the result agrees well with Berre's experiment. The attenuation plotted against the magnetic field direction has 3 peaks which are explained in terms of the geometry of the Fermi surface of Al.     

Ultrasonic study of dysprosium in a magnetic field

The ultrasonic attenuation of longitudinal waves propagating along the c axis of single crystal dyprosium is reported, as a function of the applied basal plane field in the paramagnetic region, and as a function of the temperature, at constant applied basal plane field, in the spin-spiral region. In the paramagnetic region, anomalous attenuation behavior is explained on the basis of competing spin-polarization and spin-fluctuation effects. Two anomalous maxima in the temperature dependence of the attenuation were observed: one near T_N is attributed to spin fluctuations associated with short range ferromagnetic ordering; another one at 130 K is attributed to a magnetic phase transition from a fanstructure phase, intermediate between the spin-spiral and ferromagnetically ordered phase     

Ultrasonic attenuation near the phase transition for the magnetic field induced excitonic phase in bismuth

The fluctuation contribution to the ultrasonic attenuation above T_c is shown to have a log T form similar to the log T components in properties of Kondo systems. The recent results by Mase et al. show this behaviour in bismuth.     

Ultrasonic attenuation in a LiIO3 crystal

The temperature dependences of the attenuation of longitudinal acoustic waves along the x axis of a LiIO₃ crystal are studied experimentally by the method of Bragg diffraction of light by ultrasound. The measurements are performed in the temperature range from 215 to 335 K at frequencies of 400–690 MHz. Above 260 K, the attenuation is found to exhibit a frequency-independent growth of a relaxational character, which is used to calculate the enthalpy of the activation of ionic motion in the direction normal to the hexagonal axis. In addition, resonance attenuation peaks are observed; as the frequency increases, the peaks are shifted toward lower temperatures. A phenomenological model is proposed to explain the origin of the resonance absorption.     

Ultrasonic attenuation in aluminium

Second- and third-order elastic-constant data have been used to determine the Grüneisen mode, 〈γ〉, average-square Grüneisen constant, 〈γ²〉 and nonlinearity constant D, for Aluminium. The attenuation suffered by longitudinal ultrasonic wave propagating in 〈100〉 and 〈110〉 directions and shear wave polarized along 〈100〉 and 〈1$\text{1}$0〉 directions, due to phonon viscosity and thermoelastic phenomena have been evaluated from two different values of TOEM at 289°K and comparison with observed experimental results has been made also.     

Ultrasonic attenuation in pearlitic steel

Expressions for the attenuation coefficients of longitudinal and transverse ultrasonic waves are developed for steel with pearlitic microstructure. This type of lamellar duplex microstructure influences attenuation because of the lamellar spacing. In addition, longitudinal attenuation measurements were conducted using an unfocused transducer with 10 MHz central frequency on the cross section of a quenched railroad wheel sample. The dependence of longitudinal attenuation on the pearlite microstructure is observed from the changes of longitudinal attenuation from the quenched tread surface to deeper locations. The results show that the attenuation value is lowest and relatively constant within the quench depth, then increases linearly. The experimental results demonstrate a reasonable agreement with results from the theoretical model. Ultrasonic attenuation provides an important non-destructive method to evaluate duplex microstructure within grains which can be implemented for quality control in conjunction with other manufacturing processes.     

Ultrasonic attenuation in insulating crystals

A theory for the dampingΓ of ultrasonic waves due to three-phonon processes is developed by using a Green's function method. The imaginary part of the self-energy of the impressed ultrasound phonons interacting with thermal phonons is calculated. In the limits ofω τ very large and very small the known results are rederived, whereω is the frequency of the ultrasonic wave andτ the thermal phonon relaxation time. The intermediate range ofω τ values is discussed in detail for the case of longitudinal phonon attenuation. It is found, that forω τ>1 a Landau-Rumer type law applies also for longitudinal phonons,Γ～ωT ⁴. But it is shown that dispersion effects and large third-order elastic anisotropy can lead to a stronger temperature dependence thanT ⁴ and a weaker dependence on frequency thanω. These results are compared with recent experiments.     

The attenuation of oscillatory thermocapillary convection in the oxide melt by a transverse magnetic field

The effect of a transverse magnetic field on the oscillatory thermocapillary convection in the NaBi(WO4)2 melt was studied by using the in-situ observation system. The oscillation was attenuated when the 60 mT magnetic field was applied, as shown by the decrease in the amplitude and the frequency. Furthermore, the oscillation under smaller temperature difference was stabilized after the magnetic field was applied. The magnetic effect could be due to the Lorentz force generated by the interaction between motional ions and the vertical magnetic field. The ionic conductivities were measured to demonstrate the effect of the magnetic field. The solid ionic electrical conductivity increases with the temperature rise, and the melt ionic electrical conductivity was measured to be about 2.0×10-4 Ω-1·cm-1. Experimental results manifest that the effect of the magnetic field on anions and cations in the melt makes the flow change to the direction normal to the applied field, so the flow is more orderly and the oscillation is suppressed.     

Crystal field interaction in erbium garnets

A crystal field analysis has been performed for erbium aluminum garnet (ErAG) and erbium gallium garnet (ErGG). Good agreement between the measured and calculated energy levels was obtained.     

Ultrasonic attenuation in plasma-sprayed coating materials

Measurements have been made of the attenuation in thin samples of plasma-sprayed molybdenum, nickel aluminide and aluminium coating materials in the frequency range 2.5 to 15 MHz. It has been found that attenuation is dependent on the structure of the coatings and in particular on porosity. Interference effects in such thin samples are shown to be unimportant because of their high attenuations. An analysis of ultrasonic attenuation through thin samples is presented.     

The magnetic properties of erbium vanadate

ErVO₄, erbium vanadate, is a tetragonal paramagnet which is known to order magnetically below about 0.4 K. The nature of the ordered structure is predicted from earlier measurements on other vanadates containing neighbouring lanthanide ions. The effects of applied magnetic fields are also discussed.     

Spectroscopic study of a brush cathode plasma in a magnetic field

The brush cathode helium discharge in the magnetic field has been operated stably at discharge currents larger than those without magnetic field. The diameter of the plasma column has been determined by the configuration of the magnetic field. The measurements of the spectral intensities of the recombination continuum followed by the 2³S-n³P series reveals that the electron density is 1·8 × 10¹³ cm^-3 and the electron temperature is 0·17 eV at a discharge current of 500 mA and a pressure of 0·9 torr for a magnetic flux density of 1·3 kG. The principal quantum number for line merging is 20.