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1
Content available remote

Magnetic Field Influence on Critical Sound Attenuation and Velocity Variation in Ferromagnets

100%
Pawlak A.
Acta Physica Polonica A
|
2009
|
vol. 115
|
issue 1
229-231
EN
The ultrasound velocity and attenuation are investigated in ferromagnets under an application of magnetic field. In the magnetic field six different characteristic regimes are distinguished instead of traditional two (hydrodynamic and critical) found for the case of zero magnetic field. The mean-field Landau-Khalatnikov theory as well as the scaling predictions are given for each regime. Various critical exponents are identified for these regions and compared with the ultrasonic data for MnP. The shift of the ultrasonic attenuation peak under the influence of magnetic field towards higher temperatures is discussed.
2
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Magnetic Field Effect on Sound Propagation in Antiferromagnets

100%
Pawlak A., Fechner B.
Acta Physica Polonica A
|
2009
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vol. 115
|
issue 1
232-234
EN
On the basis of the theory of phase transitions, a model describing anomalies of sound attenuation coefficient close to the antiferromagnet-paramagnet phase transition in magnetic field was developed. The scaling behaviour of the sound velocity and attenuation coefficient was determined. The physical origin of the two-peak structure in the field dependent ultrasound attenuation observed in a number of antiferromagnets was identified. The theoretical results were compared with experimental results obtained for terbium.
3
Content available remote

Diffusive Regime for Critical Sound Attenuation and Dispersion in Magnets

100%
Pawlak A., Błaszak M.
Acta Physica Polonica A
|
2000
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vol. 97
|
issue 5
905-908
EN
We consider a new regime of sound propagation in magnetic systems above the critical point. On the basis of a general statistical model including a flow of energy between spin and lattice subsystems we found that there is a region of parameters where the sound attenuation and dispersion can be expressed in a similar way as for noncritical systems for which only the heat conduction matters. Contrary to the case of the classical heat diffusion in the critical magnetic system both the specific heat, entering the reduced frequency, as well as the effective amplitude are frequency and temperature dependent reflecting the critical singularities present in the system near its critical point.
4
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Critical Sound Propagation in Magnetic Metals and Bottleneck Phenomena

100%
Pawlak A.
Acta Physica Polonica A
|
2000
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vol. 97
|
issue 5
909-912
EN
A semiphenomenological model of sound propagation in a critical magnetic system is proposed, which takes into account a relaxation of energy between the system of localised spins and the conduction electron spins as well as the coupling of the longitudinal phonon to bilinear combination of spin fluctuations and to the energy densities. A general expression for the acoustic self-energy is obtained within the one-loop approximation. The effect of "bottlenecking" and its influence on the critical singularities in the sound characteristics is discussed.
5
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Spin-Lattice Relaxation Effects in Critical Sound Propagation

100%
Pawlak A.
Acta Physica Polonica A
|
1997
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vol. 92
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issue 2
449-452
EN
The nonasymptotic critical properties of sound propagation are studied in compressible Ising system above T_{C}. In the present paper we analyse a model where in addition to the coupling to two order-parameter fluctuations the sound mode couples linearly to the fluctuations of spin-energy and lattice-energy densities. Both subsystems exchange energy with the rate determined by the bare spin-lattice relaxation time. The total energy may be conserved or not. The crossover between insulator-like behaviour ~t^{-2α} and metal-like behaviour ~t^{-(zν+α)} in ultrasonic attenuation is investigated according to the value of ultrasonic frequency, the reduced temperature t, bare relaxation times and various coupling constants.
6
Content available remote

Theory of Critical Sound Attenuation in Ising-Type Magnets

100%
Pawlak A.
Acta Physica Polonica A
|
2000
|
vol. 98
|
issue 1-2
23-39
EN
The critical behaviour of sound attenuation has been studied in an elastically isotropic Ising system above the critical point on the basis of a complete stochastic model including both spin-energy and lattice-energy modes linearly coupled to the longitudinal sound mode. The effect of spin-lattice relaxation on the ultrasonic attenuation is investigated. The crossover between Kawasaki behaviour and Murata-Iro-Schwabl behaviour is studied as dependent on the values of ultrasonic frequency, reduced temperature, relaxation times, etc. A new high-frequency regime is discussed in the magnetic systems. This new regime corresponds to an adiabatic sound propagation and is very similar to the ones in binary mixture and liquid helium. A new frequency-dependent specific heat being the harmonic average of the bare lattice and critical spin specific heats is introduced. It was shown that such specific heat describes the process of equilibration between spin and lattice subsystems and includes the most important features of critical sound attenuation.
7
Content available remote

Ultrasonic Attenuation in Alloys

100%
Kor S., Singh R.
Acta Physica Polonica A
|
1993
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vol. 83
|
issue 6
751-758
EN
Ultrasonic attenuation was evaluated in metallic alloys, Ni_{x}Cu_{1-x} (x = 1.00, 0.70, 0.60, 0.45 and 0) due to phonon-phonon (p-p) interaction and thermoelastic loss in a wide temperature region along ⟨110⟩ crystallographic direction for longitudinal and shear waves. Ultrasonic Grüneisen parameters, nonlinearity constants and ultrasonic attenuation due to p-p interaction and thermoelastic loss were determined from 50 K to 500 K using the Born-Mayer and electrostatic potentials. The results were compared with available experimental results.
8
Content available remote

A Photoacoustic Study of Zn_{1-x}Mg_{x}Se Mixed Crystals

100%
Męczyńska H., Zakrzewski J., Łęgowski S., Popielarski M., Firszt F., Szatkowski J., Klugiewicz R., Łęgowski K.
Acta Physica Polonica A
|
1995
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vol. 87
|
issue 2
547-550
EN
The photoacoustic spectroscopy with a piezoelectric transducer was em­ployed to evaluate the band gaps of a series of Zn_{1-x}Mg_{x}Se mixed crystals of different composition. The photoacoustic measurements performed at room temperature yield information about the quality of the samples. The photoa­coustic spectra were measured using the continuous wave and nanosecond pulse excitation.
9
Publication available in full text mode
Content available

Sound Attenuation at High Temperatures in Pt

100%
Singh R., Pandey K.
Acta Physica Polonica A
|
2006
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vol. 109
|
issue 2
219-228
EN
Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss was evaluated in VIII group transition metal Pt in a wide temperature range (100 K to 1500 K) for longitudinal and shear waves along〈100〉, 〈110〉 and〈111〉 directions and for shear waves polarised along different directions. Electrostatic and Born-Mayer potentials were used to obtain second and third order elastic constants, taking nearest-neighbour distance and hardness parameter as input data. Second and third order elastic constants data obtained at different temperatures were used to obtain Gruneisen parameters and non-linearity or anisotropy parameters which in turn were used to evaluate (α/f^2)_l and (α/f^2)_s in Akhiezer regime. The results were discussed and it was found that at lower temperatures (α/f^2) increases rapidly with temperature and then rate of increase becomes very small. Contribution to the total attenuation due to thermoelastic loss is negligible so that due to phonon-phonon interaction establishing that major part of energy from sound wave is removed due to interaction with thermal phonons (lattice vibrations).
10
Content available remote

Magnetic Field Dependence of Critical Attenuation in Ferromagnet

100%
Pawlak A.
Acta Physica Polonica A
|
2012
|
vol. 121
|
issue 5-6
1185-1187
EN
The influence of magnetic field on the sound attenuation is investigated in ferromagnets. With the aid of the Nelson method we derive frequency-, magnetic field- and temperature-dependent expression for the sound attenuation coefficient near a critical point in the Ising-type system. The shift of the ultrasonic attenuation peak under the influence of magnetic field towards higher temperatures is discussed.
11
Content available remote

Critical Sound Attenuation and Spin-Lattice Relaxation

100%
Pawlak A.
Acta Physica Polonica A
|
1994
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vol. 85
|
issue 2
385-387
EN
The nonasymptotic critical properties of sound propagation are studied in compressible magnetic system. The role of coupling of order parameter and acoustic phonons to spin-energy density is investigated and the ultrasonic attenuation scaling function is found.
12
Content available remote

Ultrasonic Attenuation in Binary Alloys

80%
Kor S., Pandey G.
Acta Physica Polonica A
|
1998
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vol. 93
|
issue 3
491-497
EN
An attempt was made to study the ultrasonic attenuation in Cu-Zn, Ag-Cd, Ag-Mg and Ag-Zn alloys, due to phonon-phonon interaction at 300 K. The Morse potential was used to evaluate the second and third order elastic constants. How far the neighbouring atoms are effective and contributing to ultrasonic attenuation was studied. It is concluded that most of the ultrasonic attenuation is covered by the atoms from 1st to 8th shell. The contribution to ultrasonic attenuation due to 9th shell to 12th shell is very small. It is also concluded that alloys behave more or less in the same manner as metals.
13
Content available remote

Optical and Structural Properties of Zn_{1-x}Be_{x}Se Mixed Crystals

80%
Firszt F., Łęgowski S., Męczyńska H., Szatkowski J., Zakrzewski J., Paszkowicz W., Domagała J., Marczak M.
Acta Physica Polonica A
|
1998
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vol. 94
|
issue 2
309-312
EN
Optical and structural properties of Zn_{1-x}Be_{x}Se bulk crystals in the range of composition 0 ≤ x ≤ 0.41 have been studied. These crystals were grown by Bridgman method under an argon overpressure. Transmission, absorption, photoluminescence and photoacoustic spectra as a function of composition were investigated. It has been found that the crystal structure is of sphalerite type. The crystal quality increases when the crystallization process of the same boule is performed more than once. In the investigated composition range the lattice constant decreases and the energy gap increases with increasing beryllium content. From photoluminescence measurements the excitonic energy gap about 3.64 eV at 40 K was estimated for the highest obtained Be concentration (x=0.41).
14
Content available remote

Acoustical Dissipation in Some Tetrahedrally-Bonded Semiconducting Compounds

80%
Kor S. K., Mehrotra P.
Acta Physica Polonica A
|
1995
|
vol. 87
|
issue 6
981-983
EN
Phonon-phonon coupling and thermoelastic relaxation are the principal thermal causes of ultrasonic attenuation in solids at room temperature. Sec­ond order elastic moduli and third order elastic moduli have been used to study the ultrasonic attenuation suffered by compressional and shear acous­tic waves for some tetrahedrally bonded semiconducting materials, viz. GaP, InP and InAs along ⟨100⟩, ⟨110⟩ and ⟨111⟩ crystallographic directions. At­tenuation in case of InP is found to be quite large as compared to GaP and InAs. The reason behind this discrepancy is due to doping of Cr in InP sam­ple and it is also seen that ultrasonic attenuation due to phonon-phonon interaction dominates over that due to thermoelastic relaxation.
15
Content available remote

Acoustic-Emission Study of Intermittency of Plastic Flow during Twinning and Dislocation Glide

80%
Shashkov I., Lebedkina T., Lebyodkin M., Dobron P., Chmelik F., Kral R., Parfenenko K., Mathis K.
Acta Physica Polonica A
|
2012
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vol. 122
|
issue 3
430-434
EN
Recent studies of plastic deformation with the aid of acoustic emission techniques proved an intermittent, scale-invariant character of plastic processes, as reflected in power-law statistical distributions. In some cases, the power-law exponents display close values leading to hypothesis of universality of scaling laws for various mechanisms of plasticity. Nevertheless, the accurate determination of the power law may be impeded by some sources of errors inevitable in real conditions, in particular, by superposition of individual acoustic emission events. In the present work, the sensitivity of the apparent statistics to the variation of the parameters of individualization of acoustic emission events is examined using Mg and Al based alloys. Both these alloys exhibit a highly cooperative character of plastic deformation, leading to strong acoustic activity which is governed by distinct microscopic mechanisms - mechanical twinning and the Portevin-Le Chatelier effect, respectively.
16
Content available remote

Luminescence Quantum Efficiency of Mn^{2+} States in ZnSe:Mn as Studied by means of Photoacoustic Spectroscopy

80%
Męczyńska H., Łęgowski S., Dąbrowska W., Popielarski M., Ogielski Z., Zakrzewski J.
Acta Physica Polonica A
|
1993
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vol. 84
|
issue 4
823-825
EN
The photoacoustic spectroscopy with a piezoelectric transducer was employed to determined the quantum efficiency for low Mn concentration in ZnSe monocrystals. The photoacoustic spectra were measured using the continuous wave excitation and nanosecond pulse method.
17
Content available remote

Intermittency and Deformation Band Propagation in an Austenitic FeMnC TWIP Steel

80%
Lebyodkin M., Lebedkina T., Roth A., Allain S.
Acta Physica Polonica A
|
2012
|
vol. 122
|
issue 3
478-481
EN
Plastic deformation of austenitic FeMnC TWIP steels exhibits complex spatiotemporal patterns associated with the occurrence of deformation bands and the concomitant fluctuations of the deforming stress. Although the plastic instability is a generic property of these steels and is usually attributed to interaction of dislocations with solutes (the Portevin-Le Chatelier effect), both the kinematics of the deformation bands and the characteristic shape of stress serrations observed in the carbon-containing TWIP steel at room temperature manifest unusual features. The nature of these peculiarities and the mechanism of jerky flow in such steels are unclear. In the present work, an attempt is made to get an insight into the jerky flow in the Fe22Mn0.6C steel by studying the time series characterizing the evolution of plastic deformation at various scales: stress-time curves, local strain field, and acoustic emission accompanying the deformation processes. Stress and strain fluctuations related to two distinct scale ranges are detected and characterized.
18
Publication available in full text mode
Content available

Size Dependent Acoustical Properties of bcc Metal

80%
Yadav R., Pandey D.
Acta Physica Polonica A
|
2005
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vol. 107
|
issue 6
933-946
EN
The ultrasonic attenuation is evaluated at 300 K along [100], [110], and [111] directions for the characterization of bcc metal Ta. The size of the metal is considered in nanorange. Ultrasonic velocity, Grüneisen parameter and acoustic coupling constant that depend on second and third order elastic constants are calculated for determination of ultrasonic attenuation coefficient. Second and third order elastic constants of the bcc metal Ta at nanoscale at 300 K are also calculated starting with only two basic parameters. For the information about defects at nanoscale, the dislocation drag coefficients are calculated for the metal at different size along [100] orientation. The ultrasonic attenuation increases with the size of material as the size variation of the thermal conductivity and the thermal relaxation time. There is significant increase in the attenuation up to 150 nm.
19
Content available remote

Photoacoustic Investigation of Absorption Edge of Cd_{1-x}Mg_{x}Se Mixed Crystals

80%
Firszt F., Łęgowski S., Męczyńska H., Sekulska B., Szatkowski J., Zakrzewski J., Paszkowicz W.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 4
749-752
EN
The Cd_{1-x}Mg_{x}Se crystals were grown by modified Bridgman method for x ranging from 0 to 0.44. The photoacoustic spectroscopy was employed for evaluation of the band gaps of series Cd_{1-x}Mg_{x}Se mixed crystals with different composition. The photoacoustic spectra were measured at 300 K and 90 K using continuous wave excitation in the range from 400 nm to 800 nm. The increase in the band-gap energy with increasing Mg content is observed. The photoacoustic results are compared with photoluminescence and transmission spectra.
20
Content available remote

Photoluminescence and Photoacoustic Investigations of Beryllium and Magnesium Containing Wide Gap II-VI Mixed Crystals

70%
Firszt F., Łęgowski S., Męczyńska H., Sekulska B., Szatkowski J., Zakrzewski J., Paszkowicz W.
|
|
vol. 95
|
issue 6
991-996
EN
Zn_{1-x}Be_{x}Se, Cd_{1-x}Mg_{x}Se and Zn_{1-x-y}Be_{x}Mg_{y}Se mixed crystals grown from the melt with different concentrations of Be and Mg have been characterized by photoluminescence and photoacoustic methods. An increase in band gap energy with increasing Be and Mg contents was observed. The photoacoustic spectroscopy was also employed for evaluation of thermal diffusivity of mixed Zn_{1-x}Be_{x}Se crystals with different beryllium contents.
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