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Vortex pinning behaviour in MgB2 bulk samples obtained by electric-field assisted sintering

L. MIU1,* , I. IVAN1, G. ALDICA1, P. BADICA1, J. R. GROZA2, D. MIU3, G. JAKOB4, H. ADRIAN4

Affiliation

  1. National Institute of Materials Physics, 77125 Bucharest-Magurele, P. O. Box MG-7, Romania
  2. Department of Chemical Engineering and Materials Science, University of California, Davis, 95616-5294 California, USA
  3. National Institute for Laser, Plasma, and Radiation Physics, 77125 Bucharest-Magurele, P. O. Box MG-36, Romania
  4. Institute of Physics, University of Mainz, 55128 Mainz, Germany

Abstract

Well-compacted MgB2 specimens with the density higher than 90 % of the theoretical value were obtained by electric-field assisted sintering. This method assures a good grain connectivity, which leads to the appearance of efficient pinning centres at the grain boundaries. We measured the DC magnetization curves and the relaxation of the irreversible magnetization using the SQUID magnetometry for a magnetic field H up to 50 kOe applied in zero-field-cooling conditions. The critical current density is of the order of 1010 A/m2 at H = 20 kOe and T = 10 K. A crossover plastic creep at high temperatures T – elastic creep at low T described by H ∝ T −2 in the low T – high H domain was observed. This is caused by the macroscopic currents induced in the sample during magnetization measurements. By decreasing T below this line the determined creep exponent rapidly overcomes the widely accepted theoretical values for elastic (collective) pinning. This behaviour can be explained through the occurrence of micro flux jumps, which seem to be responsible for the finite magnetization relaxation rate in the low-T limit. The relaxation of the irreversible magnetization allowed us the precise determination of the characteristic pinning energy barrier..

Keywords

Superconductors, MgB2, Electric-field assisted sintering, Vortex pinning, Magnetization relaxation.

Submitted at: Sept. 1, 2008
Accepted at: Nov. 11, 2008

Citation

L. MIU, I. IVAN, G. ALDICA, P. BADICA, J. R. GROZA, D. MIU, G. JAKOB, H. ADRIAN, Vortex pinning behaviour in MgB2 bulk samples obtained by electric-field assisted sintering, Journal of Optoelectronics and Advanced Materials Vol. 10, Iss. 11, pp. 2976-2980 (2008)