MgB
                  2
              :
           Synthesis, sound velocity, and dynamics of the vortex phase

Ignatova, T. V.; Zvyagina, G. A.; Kolobov, I. G.; Masalitin, E. A.; Fil, V. D.; Paderno, Y.; Bykov, A. N.; Paderno, V. N.; Lyashenko, V. I.

doi:10.1063/1.1468522

Cited by 13 publications

(6 citation statements)

References 14 publications

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“…7 This means heat transport by phonons can be ruled out for the avalanches. A covering layer of aluminum or gold with a thickness of several microns is able to suppress the propagation of the avalanches 8 and to recover the critical current density.…”

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confidence: 99%

Bending of magnetic avalanches in MgB2 thin films

Albrecht¹,

Matveev²,

Djupmyr³

et al. 2005

Applied Physics Letters

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The penetration of magnetic flux into a superconductor above the lower critical field does not necessarily happen in a regular way. It is found that under particular conditions, a chaotic penetration in form of magnetic avalanches occurs. These avalanches are closely related to the so-called thermomagnetic instability, which identifies local heating due to flux line movement as the origin of the effect. In case of MgB2 thin films, these avalanches are found only below T=10K and are suppressed by a covering metallic layer with high thermal conductivity and sufficient thickness. These avalanches are observed in the case of partly gold covered MgB2 films by the magneto-optical Faraday effect. The investigation of avalanches propagating into a gold-covered region revealed a change of the propagation direction depending on the incident angle of these avalanches.

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confidence: 99%

Bending of magnetic avalanches in MgB2 thin films

Albrecht¹,

Matveev²,

Djupmyr³

et al. 2005

Applied Physics Letters

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“…͑1͒, as it was done before for MgB 2 . 7 We use the working frequency /2 ϳ 55 MGz. Details of the measuring procedure are described in Ref.…”

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confidence: 99%

Surface pinning in an amorphous ZrTiCuNiBe alloy

Fil

Avramenko

et al. 2005

Phys. Rev. B

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We have measured the amplitude and the phase of an electromagnetic ͑EM͒ field radiated from a superconductor ͑amorphous ZrTiCuNiBe alloy͒ in the mixed state due to the interaction of the flux lattice with an elastic wave. The results point to an essential contribution of a surface pinning into the flux lattice dynamics. We propose a model that describes radiation of the EM field from superconductors with nonuniform pinning. The model allows us to reconstruct the viscosity and the Labusch parameters from the experimental data. The behavior of the Labusch parameter can be qualitatively explained in terms of the collective pinning theory with the allowance of thermal fluctuations. Soft type-II superconductors were studied intensively during last four decades with the goal to investigate various aspects of vortex matter dynamics ͑see the comprehensive review by Brandt 1 ͒. Nevertheless, many questions that require further investigation remain. Among these questions is the problem of relation between the surface and the bulk pinning. Up to now the dynamics of the vortex state in such an exclusively nonuniform situation was studied by the surface impedance method. 2 In this paper, on the example of amorphous Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 alloy we demonstrate abilities of a method based on excitation of vortex lattice oscillations by a high-frequency sound wave.The essence of the method is the following. A superconductor situated in the lower half space ͑z Ͻ 0͒ is subjected by a constant magnetic field H ʈ z. A transverse elastic wave propagating along H and polarized in x direction produces transverse ͑with respect to H͒ oscillations of the vortex lattice caused by pinning and viscous friction, and, consequently, induces an electromagnetic ͑EM͒ field. An antenna receives the EM field ͑with E y and H x components͒ radiated through the elastically free surface of the sample ͑the surface perpendicular to the direction of propagation of the elastic wave͒. While a similar experimental setup was already applied for the study of type-II superconductors, 3,4 the key point is measuring both the amplitude and the phase of the EM field ͑more accurately, the changes of these quantities͒.In the uniform case and in the local limit ͑q Ӷ l −1 , q is the wave number and l is the mean-free path͒ the components of the EM field at z = 0 are given by a simple expression, 5,6where u͑z͒ = u 0 cos qze i t is the displacement in the elastic wave, k 2 is the square of the complex wave number of the EM field in a conductor, and c is the light velocity. Equation ͑1͒ is applicable for the normal as well as the superconducting state of the metal. In the normal state k 2 = k n 2 =4 i 0 / c 2 ͑ 0 is the static conductivity in the normal state͒ is imaginary valued quantity. In the superconducting state at small magnetic fields͑ L is the London penetration length͒ is real valued. At such fields the phase of the EM signal is a constant and we use its value as the reference point. In the well-developed Shubnikov statewhere Ͼ 0 is the viscosity p...

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“…We begin with the discussion of phonon behaviour and electronic of specific heat. The input data (r 0 , b) for Mg 12x Al x B 2 (x ¼ 0, 0.1, 0.2) at room temperature are obtained by using the Vegard's law [26] and the data on them for MgB 2 Mg 12x Al x B 2 x ¼ 0, 0.1, 0.2, [4,6,8,27,28] materials. Using these input data and the van der Waals coefficients (c kk 0 and d kk 0 ) evaluated from the Slater and Kirkwood method [23] for MgB 2 , we have obtained the model parameters (b 1 , b 2 , r 1 and r 2 ) using the equilibrium condition and Bulk modulus relation (Equations (8) and (9)).…”

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confidence: 99%

Normal and superconducting state specific heat of Mg_1 − xAl_xB₂(0 < x < 0.2)

Varshney

Bhatnagar

Varshney³

et al. 2014

Molecular Simulation

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A theoretical analysis of specific heat C(T) behaviour of the Mg 12x Al x B 2 (0 , x , 0.2) in the temperature domain 0 # T # 300 K is presented. Calculations of C(T) have been made within the two-component scheme: one is the phonon and the other is the electronic contribution. Phonon specific heat is well estimated from the Debye and Einstein temperature for Mg 12x Al x B 2 obtained following an overlap repulsive potential. The interatomic potential of this model includes contributions from the long-range Coulomb attraction and the short-range overlap repulsion and the van der Waals attraction. The fermion constituent as the electronic specific heat is deduced using a suitable trial function above and below T c . At the critical temperature, the discontinuity in specific heat is higher than that of other samples and the transition is sharper than for most samples. The theoretical results from boson and fermion terms are then compared with the experimental results.

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MgB 2 : Synthesis, sound velocity, and dynamics of the vortex phase

Cited by 13 publications

References 14 publications

Bending of magnetic avalanches in MgB2 thin films

Bending of magnetic avalanches in MgB2 thin films

Surface pinning in an amorphous ZrTiCuNiBe alloy

Normal and superconducting state specific heat of Mg_1 − xAl_xB₂(0 < x < 0.2)

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MgB 2 : Synthesis, sound velocity, and dynamics of the vortex phase

Cited by 13 publications

References 14 publications

Bending of magnetic avalanches in MgB2 thin films

Bending of magnetic avalanches in MgB2 thin films

Surface pinning in an amorphous ZrTiCuNiBe alloy

Normal and superconducting state specific heat of Mg1 − xAlxB2(0 < x < 0.2)

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Normal and superconducting state specific heat of Mg_1 − xAl_xB₂(0 < x < 0.2)