Fishtail and vortex dynamics in the Ni-doped iron pnictide BaFe<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mrow><mml:mn>1.82</mml:mn></mml:mrow></mml:msub></mml:math>Ni<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mrow><mml:mn>0.18</mml:mn></mml:mrow></mml:msub></mml:math>As<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub

Salem‐Sugui, S.; Ghivelder, L.; Alvarenga, A. D.; Cohen, L. F.; Luo, Huiqian; Lu, Xingye

doi:10.1103/physrevb.84.052510

Cited by 28 publications

(48 citation statements)

References 29 publications

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“…It is therefore reasonable to see a rather robust field dependence of transport J c at 4.2 K. We find two stages of vortex relaxation. As shown in Fig.1(d), the initial nonlogarithmic stage with a slower relaxation rate is due to a transient effect [14] which is commonly observed in M(t ) curves [15]. In the second stage, the magnetization depends logarithmically on time, consistent with the model of thermally activated vortex motion.…”

supporting

confidence: 76%

Slow Vortex Creep Induced by Strong Grain Boundary Pinning in Advanced Ba122 Superconducting Tapes*

Dong

Huang

2019

Chinese Phys. Lett.

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We report the temperature, magnetic field and time dependences of magnetization in advanced Ba122 superconducting tapes. The sample exhibits a peculiar vortex creep behavior. Below 10 K, the normalized magnetization relaxation rate S=dln(-M)/dln(t) shows a temperature insensitive plateau with a value comparable to that of the low temperature superconductors, which can be explained within the framework of the collective creep theory. It then enters into a second collective creep regime when the temperature increases. Interestingly, the relaxation rate below 20 K tends to saturate with the increasing field. However, it changes to a power law dependence on field at a higher temperature. A vortex phase diagram composed of the collective and the plastic creep regions is concluded. Benefit from the strong grain boundary pinning, the advanced Ba122 superconducting tape has promising potential to be applied not only in liquid helium but also in liquid hydrogen or at the temperature accessible with cryocoolers.PACS numbers: 74.25. Qt, 74.25.Sv, 84.71.Mn Understanding the behavior of vortex matter in a superconductor is vitally important for both basic physics and technological applications. Vortex creep caused by thermal fluctuation introduces measurable dissipation and a reduction of the maximum loss-less current. The scale of the thermal fluctuation is usually parameterized by the dimensionless Ginzburg number Gi∝γ 2 T c 2 λ 4 /ξ 2 , where γ is the anisotropy parameter, T c is the superconducting transition temperature, λ is the penetration depth and ξ is the coherence length. Due to high T c , small ξ and large γ, the thermal fluctuation in cuprates is significant, giving rise to the so-called giant vortex creep [1]. It is thus a major task to reduce the detrimental effect of vortex motion in cuprates by incorporating effective pinning centers. Iron-based superconductors (IBSC), on the contrary, have larger ξ, lower γ, and consequently smaller Gi than that of the cuprates [2]. In combination with their high upper critical field H c2 and moderate T c [3], IBSC are considered as potential candidates in largescale application of superconductivity.After ten years of research and design since the discovery of IBSC, the (Ba/Sr) 0.6 K 0.4 Fe 2 As 2 superconducting tapes fabricated by the powder in tube (PIT) method [4,5] are now the prevalent materials for applied research. Up to now, the critical current density J c (4.2 K, 10 T) of the (Ba/Sr) 0.6 K 0.4 Fe 2 As 2 tape has already surpassed the practical application level [6]. Recently, we optimized the hot pressing method and enhance the transport J c to 1.5×10 5 A/cm 2 at 4.2 K and 10 T [7]. It even retains a J c of 5.4×10 4 A/cm 2 at 20 K and 5 T. It was found that the grain size is only 0.5-1 µm, much smaller than that of the Sr 0.6 K 0.4 Fe 2 As 2 counterpart [8] whose grains are *

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supporting

confidence: 76%

Slow Vortex Creep Induced by Strong Grain Boundary Pinning in Advanced Ba122 Superconducting Tapes*

Dong

Huang

2019

Chinese Phys. Lett.

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“…To obtain the U -J relationship, all the data should be made to fall on the same smooth U(J) curve by adjusting the constant C. The value of C was found to be C ¼ 25, which is consistent with the value of C found in some iron pnictides 18,22,58 and cuprate superconductors. 56 However, the experimental curves U(J, T), obtained by the Maley procedure do not lie on one smooth curve.…”

Section: Magnetic Relaxationmentioning

confidence: 77%

Flux pinning and magnetic relaxation in Ga-doped LiFeAs single crystals

Shlyk

Bischoff

Rose

et al. 2012

Journal of Applied Physics

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The effect of nonmagnetic Ga3+ impurities on structural and superconducting properties of LiFeAs single crystals has been studied. The out-of-plane magnetization of the doped material exhibits a remarkable double-peak structure. The presence of a low-field peak observed both in doped and undoped LiFeAs is suggestive of intrinsic structural defects, while a secondary high-field fishtail maximum, which shifts progressively with temperature, is associated with the extrinsic pinning centers created by Ga. The superconducting transition temperature of Ga doped LiFeAs is suppressed by about 4.8 K/at. %. However, a set of superconducting parameters including the superconducting transition temperature, the coherence length, the upper critical field, and the irreversibility field are not significantly reduced in a sample doped with 0.5 at. % Ga. At this Ga concentration, the critical current density of doped LiFeAs is about four times that of our undoped material in intermediate magnetic fields at 5 K. The scaling of the normalized pinning force density Fp = JcB vs the applied field normalized by Bmax (Bmax denotes the peak position of Fpmax) in the temperature range 5–13 K indicates a single type of predominant flux-pinning mechanism provided by Ga additions. Analysis of the temperature and field dependencies of the magnetic relaxation is consistent with the collective pinning model. The magnetic relaxation measurements combined with the peak position of the critical current density in the B-T phase diagram suggests an elastic–plastic transition of the vortex lattice at higher temperatures and fields. The observed vortex behavior of Ga doped LiFeAs strongly resembles that of YBa2Cu3O7 doped with nonmagnetic impurities.

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“…As field exceeds H sp , the plastic creep dominates and vortices are primarily pinned by extended defects such as dislocations [57,58]. Interestingly, the relaxation rate S(H) are featureless over the field range associated with the SMP in BaFe 1.82 Ni 0.18 As 2 with T c =8 K [59]. It should be pointed out that the SMP was observed at temperatures below T c /2 and vanished at higher temperatures in an inhomogeneous Ba 0.75 K 0.25 Fe 2 As 2 single crystal, where T c ranges from 22 to 28 K [60].…”

Section: B Microstructural Featuresmentioning

confidence: 98%

Doping evolution of the second magnetization peak and magnetic relaxation in (Ba1−xKx)F
Liu
¹
,
Zhou
²
,
Sun
³

et al. 2018
Phys. Rev. B
12
1
7
0
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We present a thorough study of doping dependent magnetic hysteresis and relaxation characteristics in single crystals of (Ba 1-x K x )Fe 2 As 2 (0.18≤x≤1). The critical current density J c reaches maximum in the underdoped sample x=0.26 and then decreases in the optimally doped and overdoped samples. Meanwhile, magnetic relaxation rate S rapidly increases and the flux creep activation barrier U 0 sharply decreases in the overdoped sample x=0.70. These results suggest that vortex pinning is very strong in the underdoped regime, but it is greatly reduced in the optimally doped and overdoped regime. Transmission electron microscope (TEM) measurements reveal the existence of dislocations and inclusions in all three studied samples x=0.38, 0.46, and 0.65. An investigation of the paramagnetic Meissner effect (PME) suggests that spatial variations in T c become small in the samples x=0.43 and 0.46, slightly above the optimal doping levels. Our results support that two types of pinning sources dominate the (Ba 1- * Corresponding author. Email address: yliu@ameslab.gov 2 x K x )Fe 2 As 2 crystals: (i) Strong δl pinning resulted from the fluctuations in the mean free path l and δT c pinning from the spatial variations in T c in the underdoped regime; (ii) Weak δT c pinning in the optimally doped and overdoped regime. PACS number(s): 74.70.Xa, 74.25.Wx, 74.25.Sv 3 I. INTRODUCTIONThe studies of vortex dynamics revealed many interesting phenomena in the iron pnictide superconductors. Because of the availability of large and high-quality single crystals, most of researches have been done on 122-type superconductors with ThCr 2 Si 2 structure. Similar to high T c cuprate superconductors, a pronounced second magnetization peak (SMP) was observed in magnetization hysteresis loops (MHLs) of (Ba 1−x K x )Fe 2 As 2 [1-6], Ba(Fe 1−x Co x ) 2 As 2 [3,6,7-13], BaFe 2 (As 1−x P x ) 2 [6,14-15]. One of striking features that that distinguish iron pnictide superconductors from high T c cuprate superconductors is the observation of strongly disordered vortex structure in iron pnictide superconductors by Bitter decoration [16][17][18][19][20][21][22], scanning tunneling microscopy (STM) [23][24], magnetic force microscopy (MFM) [25], small-angle neutron scattering (SANS) measurements [17][18][26][27]. Although long-range ordered vortex lattice (VL) was not observed yet, the so-called Bragg glass may exist, which is a glass but nearly as ordered as a perfect crystal. An ordered vortex structure was observed in an area of 130 50 nm 2 in optimally doped Ba 0.6 K 0.4 Fe 2 As 2 by STM measurement [28]. With a large Ba 0.64 K 0.36 Fe 2 As 2 single crystal, SANS measurement observed Bragg peaks corresponding to a long-range ordered triangular lattice below H=0.75 T. With increasing magnetic field above 0.75 T, diffraction spots smeared and gave the characteristic pattern of circles from a polycrystalline structure, which was interpreted as a vortex order-disorder transition associated with the appearance of SMP in MHLs [29]. In optimally doped BaF...

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Fishtail and vortex dynamics in the Ni-doped iron pnictide BaFe1.82Ni0.18As2

Cited by 28 publications

References 29 publications

Slow Vortex Creep Induced by Strong Grain Boundary Pinning in Advanced Ba122 Superconducting Tapes*

Slow Vortex Creep Induced by Strong Grain Boundary Pinning in Advanced Ba122 Superconducting Tapes*

Flux pinning and magnetic relaxation in Ga-doped LiFeAs single crystals

Doping evolution of the second magnetization peak and magnetic relaxation in (Ba1−xKx)F
Liu
¹
,
Zhou
²
,
Sun
³

et al. 2018
Phys. Rev. B
12
1
7
0
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Fishtail and vortex dynamics in the Ni-doped iron pnictide BaFe1.82Ni0.18As2

Cited by 28 publications

References 29 publications

Slow Vortex Creep Induced by Strong Grain Boundary Pinning in Advanced Ba122 Superconducting Tapes*

Slow Vortex Creep Induced by Strong Grain Boundary Pinning in Advanced Ba122 Superconducting Tapes*

Flux pinning and magnetic relaxation in Ga-doped LiFeAs single crystals

Doping evolution of the second magnetization peak and magnetic relaxation in (Ba1−xKx)FLiu1, Zhou2, Sun3 et al. 2018Phys. Rev. B12170View full textAdd to dashboardCite

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Product

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About

Doping evolution of the second magnetization peak and magnetic relaxation in (Ba1−xKx)F
Liu
¹
,
Zhou
²
,
Sun
³

et al. 2018
Phys. Rev. B
12
1
7
0
View full text Add to dashboard Cite