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Haberkorn, H.; Xu, M.; Meier, W.R.; Schmidt, J.; Suárez, S.; Bud’ko, S.L.; Canfield, P.C. |
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Substantial reduction of the anisotropy in the critical current densities Jcof Ni-doped CaKFe4As4single crystals by chemical and irradiation-induced disorder |
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Journal Article |
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Year |
2021 |
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Superconductor Science and Technology |
Abbreviated Journal |
Supercond. Sci. Technol. |
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34 |
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3 |
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035013 |
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We demonstrate that the anisotropy in the critical current densities, Jc, of CaK(Fe1-xNix)4As4 (x = 0, 0.015, 0.025, and 0.030) single crystals reduces with increasing chemical and irradiation-induced disorder. The magnetic field dependences of Jc are analyzed by performing magnetization measurements with H applied parallel and perpendicular to the crystallographic c-axis. The results show that undoped crystals display large anisotropies in Jc due to an enhancement of the vortex pinning with H applied parallel to the crystallographic ab-planes. This anisotropy reduces substantially as Ni addition increases. Moreover, we found that random disorder introduced by proton irradiation enhances mainly the vortex pinning for H parallel to the c-axis. Consequently, using adequate fluencies, the vortex pinning at low temperatures in both undoped and doped samples becomes close to isotropic. These results make the CaKFe4As4 system promising for applications that require isotropic Jc under magnetic fields. |
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0953-2048 |
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BT @ pedrazp @ |
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872 |
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Haberkorn, N.; Ribeiro, R.A.; Xiang, L.; Bud'ko, S.L; Canfield, P.C. |
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Title |
Superconducting properties and vortex pinning in intermetallic BaBi3 single crystals: A magnetization study |
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Journal Article |
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Year |
2023 |
Publication |
Physica C: Superconductivity and its Applications |
Abbreviated Journal |
Physica C |
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615 |
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1354387 |
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Hysteresis and magnetic relaxation measurements were performed on single crystals of BaBi3, which is an intermetallic compound exhibiting superconductivity with a critical temperature (Tc) of 5.9 K. The London penetration depth (λ) was determined to be 130 nm, and the coherence length (ξ) was estimated to be 13 nm. The critical current density (Jc) was found remarkably low, measuring 20,000 A/cm2 under self-field conditions at 1.8 K. Analysis of the pinning forces suggests vortex pinning by crystalline defects associated with volume Δk (variations in the Ginzburg-Landau parameter). The relaxation rate follows the Anderson-Kim model, and the pinning energies range from 1600 K at 0.02 T to 500 K at 0.5 T. Our study aims to advance our understanding of the connection between intrinsic superconducting properties and vortex behavior in intermetallic materials characterized by low thermal fluctuations. |
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0921-4534 |
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BT @ pedrazp @ |
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902 |
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Haberkorn, N.; Suárez, S.; Bud'ko, S.L.; Canfield, P.C. |
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Title |
Strong pinning and slow flux creep relaxation in Co-doped CaFe2As2 single crystals |
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Journal Article |
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2020 |
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Solid State Communications |
Abbreviated Journal |
Solid State Commun. |
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318 |
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113963 |
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Iron based superconductors; Single crystals; Vortex dynamics; Magnetization |
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We report on measurements of critical current densities Jc and flux creep rates S of freestanding Ca(Fe1−xCox)2As2 (x ≈ 0.033) single crystals with Tc ≈ 15.7 K by performing magnetization measurements. The magnetic field dependences of Jc at low temperature display features related to strong pinning. In addition, we find that the system displays small flux creep rates. The characteristic glassy exponent, μ, and the pinning energy, U0, display exceptional high values for pristine crystals. We find that for magnetic fields between 0.3 T and 1 T, μ decreases from ≈ 2.8 to ≈ 2 and U0 remains ≈ 300 K. Analysis of the pinning force indicates that the mechanism is similar to the observed in polycrystalline systems in which grain boundaries and random disorder produce the vortex pinning. Considering the large U0 observed in the single crystal, we attempt to improve the pinning by adding random point disorder by 3 MeV proton irradiation with a fluence of 2 × 1016 proton/cm2. The results show that, unlike other iron-based superconductors, the superconducting fraction is sharply reduced by irradiation. This fact indicates that the superconductivity in the system is extremely fragile to an increment in the disorder. The superconducting volume fraction in the irradiated crystal systematically recovers after removal disorder by thermal annealing, which evidences as to the observation of critical state in curves of magnetization versus magnetic field. No features related to a reentrant antiferromagnetic transition are observed for the irradiated sample. |
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0038-1098 |
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BT @ pedrazp @ |
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859 |
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Haberkorn, N.; Xu, M.; Meier, WR; Suárez, S.; Bud’ko, S.L.; Canfield, P.C. |
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Title |
Enhancement of critical current density in CaKFe4As4 single crystals through 3 MeV proton irradiation |
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Journal Article |
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Year |
2020 |
Publication |
Superconductor Science and Technology |
Abbreviated Journal |
Supercond. Sci. Technol. |
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33 |
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2 |
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025008 |
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We study the influence of random point disorder on the vortex dynamics and critical current densities Jc of CaKFe4As4 single crystals by performing magnetization measurements. Different samples were irradiated with a proton (p) beam at constant energy of 3 MeV to fluencies from 2 × 1015 p cm−2 to 4 × 1016 p cm−2. The results show the addition of extrinsic random point disorder enhances the Jc values at low and intermediate temperatures over the entire range of magnetic fields applied. The optimum pinning enhancement is achieved with a proton fluence of 3 × 1016 p cm−2, increasing Jc at 5 K by factors ≈5 and 14 at self-field and μ0H = 3 T, respectively. We analyze the vortex dynamics using the collective creep theory. The enhancement in Jc matches with a systematic reduction in the flux creep relaxation rates as a consequence of a gradual increase in the collective pinning energy U0. The substantial increment in Jc produced by random point disorder, reaching values of 9 MA cm−2 at 5 K and self-field, makes CaKFe4As4 a promising material for applications based on current carrying capacity at high magnetic fields. |
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0953-2048 |
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BT @ pedrazp @ |
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857 |
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Jaime, M.; Movshovich, R.; Stewart, G.R.; Beyermann, W.P.; Berisso, M.G.; Canfield, P.C. |
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Title |
Specific heat of Ce3Bi4Pt3 at 60 T |
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Journal Article |
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2001 |
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PHYSICA B |
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294 |
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240-244 |
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Kondo insulator materials such as CeRhAs, CeRhSb, YbB12, Ce3Bi4Pt3, and SmB6, are 3d, 4f and 5f intermetallic compounds. At high temperatures they behave like metals but a gap d in the conduction band opens at the Fermi energy as the temperature is reduced. It has been proposed that the formation of the low-temperature gap is a consequence of the hybridization between the conduction band and the f-electron levels. If this is true, Kondo metal physics should be recovered when the gap is closed at high magnetic fields. We report here specific heat results of Ce-3 Bi4Pt3 in DC and pulsed magnetic fields up to 60 T. We see evidence for the reduction of the gap in 18 T and a rapid increase of the Sommerfeld coefficient C-H/T\(T -->0) in 30 T > H > 40 T. Numerical results and the analysis of the data with the Coqblin-Schrieffer model prove a field-induced Kondo insulator-to-Kondo metal crossover. (C) 2001 Elsevier Science B.V. All rights reserved. |
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0921-4526 |
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ISI:000167738800057 |
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BT @ hernan @ |
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298 |
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Jaime, M.; Movshovich, R.; Stewart, G.R.; Beyermann, W.P.; Berisso, M.G.; Hundley, M.F.; Canfield, P.C.; Sarrao, J.L. |
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Closing the spin gap in the Kondo insulator Ce3Bi4Pt3 at high magnetic fields |
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Journal Article |
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2000 |
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Nature |
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405 |
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6783 |
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160-163 |
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Kondo insulator materials(1)-such as CeRhAs, CeRhSb, YbB12, Ce3Bi4Pt3 and SmB6-are 3d, 4f and 5f intermetallic compounds that have attracted considerable interest in recent years(2-5). At high temperatures, they behave like metals. But as temperature is reduced, an energy gap opens in the conduction band at the Fermi energy and the materials become insulating. This contrasts with other f-electron compounds, which are metallic at all temperatures. The formation of the gap in Kondo insulators has been proposed to be a consequence of hybridization between the conduction band and the f-electron levels(6,7), giving a 'spin' gap. If this is indeed the case, metallic behaviour should be recovered when the gap is closed by changing external parameters, such as magnetic field or pressure. Some experimental evidence suggests that the gap can be closed in SmB6 (refs 5, 8) and YbB12 (ref. 9). Here we present specific-heat measurements of Ce3Bi4Pt3 in d.c. and pulsed magnetic fields up to 60 tesla. Numerical results and the analysis of our data using the Coqblin-Schrieffer model demonstrate unambiguously a field-induced insulator-to-metal transition. |
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0028-0836 |
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ISI:000087080100043 |
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BT @ hernan @ |
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300 |
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