Magnetic relaxation measurements in the region of the second magnetization peak in aHgBa2CuO4+δ

Abstract

The temperature and magnetic-field dependence of activation energy U o (T,H) for creep has been studied in an HgBa 2 CuO 4ϩ␦ single crystal below and above the ''fishtail'' peak H sp (T). At constant temperature, U o (H) increases up to H sp / (T) and then for HϾH sp / (T) it decreases. H sp / (T) is located lower than the field H sp (T) deduced from the hysteresis loops. The decrease of the activation energy is probably indicative of a plastic-type creep of the vortex lattice. We demonstrate that the overall behavior of U o (T,H) at the second magnetization peak line H sp (T) in the phase diagram of HgBa 2 CuO 4ϩ␦ exhibits similarities with that observed in

Magnetic relaxation measurements on a heavily Pb-dopedBi2Sr2CaCuSun1, Song2, Du3 et al. 2002Phys. Rev. B7160View full textAdd to dashboardCite

“…[19][20][21][22][23]39 The minimum S occurs at Hϳ1200 G, which is smaller than H 2p ϭ1600 G. That is to say, the slowest magnetic relaxation does not occur exactly at H 2p but does prior to H 2p . The similar phenomenon was also observed by Pissas et al 40 For HϾ1200 G, S increases with increasing fields again.…”

Relaxation measurements in the regime of the second magnetization peak in Nb films

“…Since then, many experimental works confirmed this notion in YBa [4,6,10,11,18,19]. More specifically, in high-T c compounds for fields H > H * (T ) the activation energy U o follows a negative power-law U o ∝ H ν with ν ∈ [−0.5, −0.9] [7,10,13,18,19]. In our case we observed that above the "SMP" the activation energy 2 K the S/T and Uo/kB are monotonic in the whole field regime.…”

“…They proposed that for H < H * (T ) the response of vortex system was elastic, while for H > H * (T ) the increase of S (decrease of U o ) should be caused by plastic deformations of the vortex solid [7]. Since then, many experimental works confirmed this notion in YBa [4,6,10,11,18,19]. More specifically, in high-T c compounds for fields H > H * (T ) the activation energy U o follows a negative power-law U o ∝ H ν with ν ∈ [−0.5, −0.9] [7,10,13,18,19].…”

“…As a result the magnetic curves are more regular. The overall behavior resembles the SMP observed usually in high-T c superconductors [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]. For this reason we "loosely" refer to these characteristic fields as H′′ smp ′′ .…”

“…Recent magnetic studies in Nb films [1,2,3] reported the existence of a structure that reminisces of the second magnetization peak (SMP) which is usually observed in high-T c superconductors [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]. These studies concluded that for the case of Nb films the "SMP" is probably motivated by thermomagnetic instabilities (TMIs) that occur in the low-temperature regime, far below the uppercritical field [1,2,3].…”