Influence of random point defects introduced by proton irradiation on critical current density and vortex dynamics of Ba(Fe0.925Co0.075)

Abstract

In this work we analyze the influence of random point defects introduced by 3 MeV proton irradiation on the critical current density (J c ) and vortex dynamics of a Ba(Fe 0.925 Co 0.075 ) 2 As 2 single crystal. The results show that at low temperatures (T ) the irradiation produces an enhancement of J c of up to 2.6 times. However the J c (T ) retention at different magnetic fields (H ) in the elastic regime, estimated by the n exponent in J c vs (1 − (T /T c ) 2 ) n , is poorer after the irradiations due to the thermal softening of the pinning by the random point defects. We found that the elastic-to-plastic crossover and melting lines are only affected by the reduction of the superconducting critical temperature (T c ); they are exactly the same after rescaling the phase diagram by T /T c . The pinning mechanisms in the single crystals can be associated with a mixed pinning landscape that produces a modulation in S(H , T ) as a consequence of a fishtail or second peak in the magnetization.

Magnetic relaxation and collective vortex creep in FeTe 0.6 Se 0.4 single crystal

“…Actually, this temperature range is exactly the same range where S manifests a hump-like behavior. A similar effect of SMP on the magnetic relaxation rate was also reported in Co-doped BaFe 2 As 2 [7,11] and Nadoped CaFe 2 As 2 [28].…”

“…Obviously, there is a plateau in the intermediate temperature range with a high vortex creep rate S ∼ 0.03. The plateau and large vortex creep rate were also observed in YBa 2 Cu 3 O 7−δ [6], and iron-based "122" [7,11,12,28] and "1111" samples [13], which can be interpreted by the collective creep theory [6]. On the other hand, S -T curve undergoes an upturn at low temperatures especially at small fields like 5 and 10 kOe.…”

“…Magnetic relaxation measurements in IBSs reported so far have revealed that they also show giant flux creep and collective pinning, which implies that IBSs and cuprate superconductors may share common vortex physics [7][8][9][10][11][12][13]. Until now, most detailed studies about the vortex dynamics on IBSs have been performed on "122" phase since high-quality single crystals are readily available.…”

“…Until now, most detailed studies about the vortex dynamics on IBSs have been performed on "122" phase since high-quality single crystals are readily available. Especially in Co-doped BaFe 2 As 2 , it shows fast flux creep and a transition from collective to plastic creep [7,9,11,12]. In order to know if the large creep rate governed by collective flux creep is an intrinsic property of IBSs, detailed vortex dynamics studies should be done on other IBS samples.…”

Carbon nanotubes effects on the relaxation properties and critical current densities of MgB2 superconductor

“…For instance, irradiation of iron-based superconductors such as BaðFeCoÞ 2 As 2 produces increases in J c but the relaxation rates either decrease 25 or remain constant. 26 On the other hand, YBa 2 Cu 2 O 7 (YBCO) samples with vastly different J c values show very similar relaxation S(T). One exception is the case of YBCO crystals with columnar defects where, together with the increase in J c , a "peak" in S(T) occurs.…”