Flux-creep activation energy for pure and SiC doped MgB2 by ac-susceptibility measurements

Abstract

ac susceptibility measurements were performed on pure and SiC-doped MgB2 prepared by field assisted sintering technique in the temperature range between 5 and 50 K. The activation energy for flux-creep U for both samples was determined at dc-fields of 0, 0.5, and 5 T, respectively, from the frequency dependence of the imaginary part of the ac-susceptibility χ" data measured in the range 17-9997 Hz. It was found that at 0 and 0.5 T, the activation energy of the SiC-doped sample is almost half the energy of the pristine sample whereas at 5 T the activation energies of the two samples become almost equal. A similar behaviour show the Hp (T) lines as obtained from susceptibility data in the range 0-9 T. For fields lower than 7.5 T, the Hp field of the doped sample is lower than for the undoped MgB2. At ?7.5 T, the Hp(T) for SiC doped MgB2 crosses over the Hp(T) of pure MgB2 and for higher fields the doped samples exhibits a higher irreversibility Hp. This field dependence was extracted from the evolution of the χ1"(T) data. This behaviour is a consequence of the morphology of the sample with a large spread in grain size. © 2008 IOP Publishing Ltd.