Magnetic relaxation measurements on a heavily Pb-dopedBi2Sr2CaCu

Abstract

The magnetic relaxation measurements on a heavily Pb-doped Bi 2 Sr 2 CaCu 2 O 8ϩ␦ single crystal were carried out in the vicinity of both the anomalous magnetization peak H 2 p and its onset field H on at different temperatures. The results show that both the normalized magnetic relaxation rate S(ϭϪd ln M/d ln t) and the pinning potential U 0 exhibit remarkable changes near H on and H 2 p in the temperature region where H on (T) follows the relation of the disorder induced vortex lattice transition, H on (T)ϭH on (0)͓1Ϫ(T/T c ) 4 ͔ 3/2 . For both HϽH on and HϾH 2 p , S increases and U 0 decreases, respectively, with increasing magnetic fields. A negative power law of U 0 (H)ϰH Ϫ␣ was observed for both HϽH on and for HϾH 2 p . There exists a minimum in the magnetic-field dependence of S(H) and a maximum in the pinning potential U 0 (H) in the field range between H on and H 2 p . At lower temperature region where H on (T) deviates from the above relation, U 0 (H) behaves differently. The results are discussed in terms of both collective flux creep model and plastic flux creep model.

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].…”

“…Cu 3 O 7+δ and in other high-T c compounds as HgBa 2 CuO 4+δ and Tl 2 Ba 2 CaCu 2 O 8[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].…”