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1
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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
Content available remote

Critical Sound Propagation in Magnetic Metals and Bottleneck Phenomena

100%
Pawlak A.
Acta Physica Polonica A
|
2000
|
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.
3
Content available remote

Spin-Lattice Relaxation Effects in Critical Sound Propagation

100%
Pawlak A.
Acta Physica Polonica A
|
1997
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vol. 92
|
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.
4
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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.
5
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.
6
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.
7
Content available remote

Magnetic Field Effect on Sound Propagation in Antiferromagnets

64%
Pawlak A., Fechner B.
Acta Physica Polonica A
|
2009
|
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.
8
Content available remote

Diffusive Regime for Critical Sound Attenuation and Dispersion in Magnets

64%
Pawlak A., Błaszak M.
Acta Physica Polonica A
|
2000
|
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.
9
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Content available

Selection and electrophoretic characterization of Salmonella enterica subsp. enterica biocide variants resistant to antibiotics

33%
Futoma-Kołoch B., Książczyk M., Korzekwa K., Migdał I., Pawlak A., Jankowska M., Kędziora A., Dorotkiewicz-Jach A., Bugla-Płoskońska G.
Polish Journal of Veterinary Sciences
|
2015
|
issue 4
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