Pinning-Induced Vortex-System Disordering at the Origin of the Second Magnetization Peak in Superconducting Single Crystals

Ionescu

et al. 2020

Sci Rep

Self Cite

The second magnetization peak (SMP) in the fourfold symmetric superconducting single crystals (such as iron pnictides and tetragonal cuprates) has been attributed to the rhombic-to-square transition (RST) of the quasi-ordered vortex solid (the Bragg vortex glass, BVG). This represents an alternative to the pinning-induced BVG disordering as the actual SMP mechanism. The analysis of the magnetic response of BaFe2(As1−xPx)2 specimens presented here shows that the SMP is not generated by the RST. However, the latter can affect the pinning-dependent SMP onset field if this is close to the (intrinsic) RST line, through the occurrence of a “shoulder” on the magnetic hysteresis curves m(H), and a maximum in the temperature variation of the DC critical current density. These features disappear in AC conditions, where the vortex system is dynamically ordered in the RST domain, emphasizing the essential role of vortex dislocations for an efficient accommodation of the vortex system to the pinning landscape and the SMP development. The m(H) shoulder is associated with a precipitous pinning-induced proliferation of dislocations at the RST, where the BVG elastic “squash” modulus softens. The DC magnetization relaxation indicates that the pinning-induced vortex system disordering continues above the RST domain, as the basic SMP mechanism.

“…The applied field H = 30 kOe is close to the midpoint between H on and H p at T = T cr (see Fig. 3 ), which is expected using global magnetic measurements 46 .…”

Section: Resultssupporting

confidence: 71%

Second magnetization peak, rhombic-to-square Bragg vortex glass transition, and intersecting magnetic hysteresis curves in overdoped BaFe2(As1−xPx)2 single crystals

Ionescu

et al. 2020

Sci Rep

Self Cite

“…The curves exhibit a conspicuous peak at H smp that is known as the second magnetization peak (SMP). Second magnetization peaks have been reported in studies of most classes of superconductors, including low-T c [21,22], iron-based [23][24][25][26][27][28][29][30][31][32][33], and highly anisotropic [34,35] materials and other cuprates [29,[36][37][38][39] as well as previous work on Hg1201 [18,[40][41][42][43][44]. This peak is typically thought to originate from a crossover between vortex pinning regimes, such as elastic-to-plastic transitions [23,25,26,28], structural phase transitions [45][46][47][48] in the vortex lattice, or dimensional crossovers.…”

Section: Resultsmentioning

confidence: 88%

“…They further showed that this described data collected on a YBa 2 Cu 3 O 7−x crystals, in a regime in which there was other evidence of plastic dynamics, such as a decrease in U with magnetic field (whereas an increase is predicted for elastic creep). Consequently, it has become common to identify a change from elastic to plastic creep as a sudden change in slope on a log U − log(1/J) plot, identifying the plastic flow regime as U pl ∼ (1/J) p , for p < 0, and many studies have observed a sharp change in slope with (in some cases) strikingly linear behavior on both sides of the transition [23,25,29,48,[54][55][56][57][58][59][60][61][62][63]. At high temperatures and fields H > H ep in our samples, we see that the slope of the U * versus 1/J plot shown in Fig.…”

Section: B Plastic Deformations Of the Vortex Latticementioning

confidence: 99%

Plastic vortex creep and dimensional crossovers in the highly anisotropic superconductor HgBa$_2$CuO$_{4+x}$

M.¹,

Venuti²,

Gorman³

et al. 2021

Preprint

In type-II superconductors exposed to magnetic fields between upper and lower critical values, Hc1 and Hc2, penetrating magnetic flux forms a lattice of vortices whose motion can induce dissipation. Consequently, the magnetization M of superconductors is typically progressively weakened with increasing magnetic field B ∝ nv (for vortex density nv). However, some materials exhibit a nonmonotonic M (B), presenting a maximum in M at what is known as the second magnetization peak. This phenomenon appears in most classes of superconductors, including low Tc materials, iron-based, and cuprates, complicating pinpointing its origin and garnering intense interest. Here, we report on vortex dynamics in optimally doped and overdoped HgBa2CuO4+x crystals, with a focus on a regime in which plastic deformations of the vortex lattice govern magnetic properties. Specifically, we find that both crystals exhibit conspicuous second magnetization peaks and, from measurements of the field-and temperature-dependent vortex creep rates, identify and characterize phase boundaries between elastic and plastic vortex dynamics, as well as multiple previously unreported transitions within the plastic flow regime. We find that the second magnetization peak coincides with the elastic-to-plastic crossover for a very small range of high fields, and a sharp crossover within the plastic flow regime for a wider range of lower fields. We find evidence that this transition in the plastic flow regime is due to a dimensional crossover, specifically a transition from 3D to 2D plastic dynamics.

“…For this reason the SMP has been studied in many different systems, usually by means of the vortex dynamics. Since the discovery of iron-pnictide superconductors [14] the SMP has been observed in many of these systems and explained in terms of a pinning-crossover as observed for Ba(Fe-Co) 2 As 2 , (Ba-K)Fe 2 As 2 , Ba(Fe-Ni) 2 As 2 , Ca(Fe-Co)As and (Ca-La)(Fe-Co)As 2 [15,16,17,18,19,20,21,22], in terms of a phase transition in the vortex lattice as observed for Ba(Fe-Co) 2 As 2 ,LiFeAs, and BaFe 2 (As-P) 2 [23,24,25,26], and also in terms of an order-disorder transition in some compounds [27,28,29]. It is to note that all the systems mentioned above share a similar layered crystal structure which consists of a spacer layer in-between of FeAs superconducting layers.…”

Section: Introductionmentioning

confidence: 83%

Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$

Llovo,

Sóñora,

Mosqueira

et al. 2021

Preprint

We report the studies of detailed magnetic relaxation and isothermal magnetization measurements in the vortex state of the 112-type iron-pnictide Ca 0.82 La 0.18 Fe 0.96 Ni 0.04 As 2 superconductor with T c ∼ 22 K. In the isothermal M (H), a well defined second magnetization peak (SMP) feature is observed in the entire temperature range below T c for measurements with H c-axis. However, for H ab-planes, the SMP feature is suppressed at low temperatures, which might be due to 2D Josephson vortices forming at low temperatures and high magnetic fields in such an anisotropic system. A rigorous analysis considering the magnetic relaxation data for H c-axis suggests an elastic to plastic pinning crossover across H p , which also seems accompanied with a possible phase transition in vortex lattice near H p . Moreover, point disorder and surface defects are likely to be the dominant sources of pinning, which contribute to the δl-type of pinning in the sample. A high J c , in access of 10 5 A/cm 2 observed could potentially make this material technologically important.