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

Abstract

a b s t r a c tThe magnetic-field-induced variations of the microwave surface resistance, R s , have been investigated in ceramic Mg 1Àx (LiAl) x B 2 , with x in the range 0:1-0:4. The measurements have been performed on increasing and decreasing the DC magnetic field, H 0 , at fixed temperatures. At low temperatures, we have observed a magnetic hysteresis in the R s ðH 0 Þ curves in all the investigated samples. On increasing the temperature, the range of H 0 in which the hysteretic behavior is visible shrinks; however, in the sample with x ¼ 0:1 it is present up to temperatures close to T c . We show that the field dependence of R s can be quantitatively justified taking into account the critical-state effects on the fluxon lattice only in the sample with x ¼ 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.

Study of microwave surface resistance of type‐II superconductors carrying transport current

“…This theory has been generalized by Bonura et al including non‐uniform flux distribution in the superconductor 15. Bonura et al method has been verified by many experimental observations 16–18. Very recently, Yıldız et al have calculated the complicated mw hysteresis curves from the profiles of the magnetic induction inside the sample including the contribution of the Meissner current, at increasing and decreasing fields, using two different laws for the field dependence of the critical current density 19.…”