Suppression of magnetic relaxation by a transverse alternating magnetic field
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IVITY
Suppression of Magnetic Relaxation by a Transverse Alternating Magnetic Field I. F. Voloshina, A. V. Kalinova, L. M. Fishera, *, and V. A. Yampol’skiœb, ** a
All-Russia Electrical Engineering Institute, Moscow, 111250 Russia * e-mail: [email protected] b Institute of Radiophysics and Electronics, National Academy of Sciences of Ukraine, Kharkov, 61085 Ukraine ** e-mail: [email protected] Received November 8, 2006
Abstract—The evolution of the spatial distribution of the magnetic induction in a superconductor after the action of the alternating magnetic field perpendicular to the trapped magnetic flux has been analyzed. The observed stabilization of the magnetic induction profile is attributed to the increase in the pinning force, so that the screening current density becomes subcritical. The last statement is corroborated by direct measurements. PACS numbers: 74.25.Nf, 74.25.Qt DOI: 10.1134/S106377610707062X
1. INTRODUCTION The suppression of the static magnetization M by a transverse alternating magnetic field is one of the most interesting effects in the electrodynamics of vortex matter in hard superconductors. This phenomenon was first observed and interpreted by Yamafuji et al. [1–3]. If the superconducting plate is cooled in the absence of the magnetic field and then the static magnetic field perpendicular to the surface is applied, the inhomogeneous distribution of the magnetic field is established in the sample. The application of the alternating magnetic field in the sample plane significantly changes the distribution profile of the induction B. Vortices oriented perpendicularly to the plate are curved and move along the sample so that the static magnetization becomes homogeneous wherever the alternating field penetrates. This phenomenon and its consequences were theoretically studied in [4, 5]. Another cause of the suppression of the static magnetization under the action of the transverse alternating magnetic field (magnetization collapse) was analyzed in [6–9]. If the vortex length L is much larger than the penetration depth of the alternating magnetic field, the bend of the vortices is of no importance and the effect of the intersection and reconnection of vortex filaments that was predicted in [10] is of primary importance. As shown in [7–9], the effect of the intersection and reconnection of vortices ensures the formation of the uniform distribution of the magnetic induction B in the superconductor wherever the alternating magnetic field penetrates (collapse region). If the amplitude h0 of the alternating field is larger than the penetrating field Hp, the magnetic-flux distribution in the superconductor becomes completely uniform and the magnetic moment
of the sample vanishes. The collapse effect can be qualitatively described in the framework of the critical-state model: curlB = ( 4π/c )J c ( B ),
(1)
where Jc is the critical current density [11]. In the framework of this model, wherever the alternating magnetic field h0 penetrates, the critical currents screening this field appears and the pre
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