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MARIA LI VIGNI

Fluxon dynamics in Li–Al codoped MgB2 by microwave surface resistance measurements

  • Authors: Bonura, M; Agliolo Gallitto, A; Li Vigni, M; Monni, M
  • Publication year: 2010
  • Type: Articolo in rivista (Articolo in rivista)
  • Key words: MgB2 superconductor; Fluxon dynamics; Microwave surface resistance
  • OA Link: http://hdl.handle.net/10447/53682

Abstract

The magnetic-field-induced variations of the microwave surface resistance, Rs, have been investigated in ceramic Mg_(1-x)(LiAl)_xB_2, with x in the range 0.1 - 0.4. The measurements have been performed on increasing and decreasing the DC magnetic field, H0, at fixed temperatures. At low temperatures, we have observed a magnetic hysteresis in the Rs(H0) curves in all the investigated samples. On increasing the temperature, the range of H0 in which the hysteretic behavior is visible shrinks; however, in the sample with x=0.1 it is present up to temperatures close to Tc. We show that the field dependence of Rs can be quantitatively justified taking into account the critical-state effects on the fluxon lattice only in the sample with x = 0.4. On the contrary, in the samples with x < 0.4 the hysteresis exhibits an unusual shape, similar to that observed in others two-gap MgB_2 samples, which cannot be justified in the framework of the critical-state models.