Temperature and Purity Dependence of the Superconducting Critical Field,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi><mml:mn>2</mml:mn><mml:mn /></mml:mrow></mml:msub></mml:mrow></mml:math>. III. Electron Spin and Spin-Orbit Effects

Werthamer, N. R.; Helfand, Eugene; Hohenberg, P. C.

doi:10.1103/physrev.147.295

Cited by 3,192 publications

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“…H c2 (T) was determined as the field at which the moment first deviated from the background, as indicated by the dashed line. H c2 (T) appears to vary more slowly than predicted by the Werthamer-Helfand-Hohenberg model 6 (Fig. 3).…”

mentioning

confidence: 76%

Strongly linked current flow in polycrystalline forms of the superconductor MgB2

Larbalestier

Cooley

Rikel

et al. 2001

Nature

911

533

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The discovery of superconductivity at 39 K in MgB 2 1 raises many issues. One of the central questions is whether this new superconductor resembles a hightemperature-cuprate superconductor or a lowtemperature metallic superconductor in terms of its current carrying characteristics in applied magnetic fields. In spite of the very high transition temperatures of the cuprate superconductors, their performance in magnetic fields has several drawbacks 2 . Their large anisotropy restricts high bulk current densities to much less than the full magnetic field-temperature (H-T) space over which superconductivity is found. Further, weak coupling across grain boundaries makes transport current densities in untextured polycrystalline forms low and strongly magnetic field sensitive 3,4 . These studies of MgB 2 address both issues. In spite of the multi-phase, untextured, nano-scale sub-divided nature of our samples, supercurrents flow throughout without the strong sensitivity to weak magnetic fields characteristic of Josephson-coupled grains 3 . Magnetization measurements over nearly all of the superconducting H-T plane show good temperature scaling of the flux pinning force, suggestive of a current density determine d by flux pinning. At least two length scales are suggested by the magnetization and magneto optical (MO) analysis but the cause of this seems to be phase inhomogeneity, porosity, and minority insulating phase such as MgO rather than by weakly coupled grain boundaries. Our results suggest that polycrystalline ceramics of this new class of superconductor will not be compromised by the weak link problems of the high temperature superconductors, a conclusion with enormous significance for applications if higher temperature analogs of this compound can be discovered.The principal samples were synthesized by direct reaction of bright Mg flakes (Aldrich Chemical) and sub-micron amorphous B powder (Callery Chemical). Starting materials were lightly mixed in half-gram batches, and pressed into pellets. These pellets were placed on Ta foil, which was in turn placed on Al 2 O 3 boats, and fired in a tube furnace under a mixed gas of 95% Ar 5% H 2 for 1 hour at 600 C, 1 hour at 800 C, and 1 hour at 900 C, and then lightly ground. The resulting powders were pressed into pellets and then hot pressed at 10 kbar at temperatures between 650 and 800 °C for periods between 1 and 5.5 hours. Disks ~4 mm in diameter and ~1 mm thick were cut from these pellets for property characterization. As noted later, this process cannot yet be considered optimum.Magnetization properties were examined in SQUID and vibrating sample magnetometers (VSM) in applied fields up to 14 T from 4.2 to above T c . Figure 1 shows onset T c values of 37-38 K for the above samples and for commercial MgB 2 powder (99.5%, ~2 µm diameter by examination, CERAC). Sample 1 and the commercial powder show smooth transitions with some temperature dependence of the zerofield cooled (ZFC) shielded moment, while sample 3 exhibits a step, indicative of non-uniformity in su...

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mentioning

confidence: 76%

Strongly linked current flow in polycrystalline forms of the superconductor MgB2

Larbalestier

Cooley

Rikel

et al. 2001

Nature

911

533

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“…30) In this context, we expect that the SC order in the Ni-doped alloys is still governed by the Pauli-limited condition. To verify this expectation, we estimate the orbital-limited critical field at zero temperature H orb c2 (0) by using a simple relation: 39) It is found that the initial slope of H c2 (T ), (µ 0 dH c2 /dT ) T c , is roughly independent of x for x ≤ 0.20 (inset of Fig. 4), yielding the ratio H orb c2 (0)/H c2 (0) ∼ 3 for all these alloys.…”

Section: Superconducting Properties In Magnetic Fieldsmentioning

confidence: 99%

Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo₁₋_xNi_xIn₅

et al. 2016

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The effect of off-plane impurity on superconductivity and non-Fermi-liquid (NFL) behavior in the layered heavyfermion compound CeCo 1−x Ni x In 5 is investigated by specific heat, magnetization, and electrical resistivity measurements. These measurements reveal that the superconducting (SC) transition temperature T c monotonically decreases from 2.3 K (x = 0) to 0.8 K (x = 0.20) with increasing x, and then the SC order disappears above x = 0.25. At the same time, the Ni substitution yields the NFL behavior at zero field for x = 0.25, characterized by the − ln T divergence in specific heat divided by temperature, C p /T , and magnetic susceptibility, M/B. The NFL behavior in magnetic fields for x = 0.25 is quite similar to that seen at around the SC upper critical field in pure CeCoIn 5 , suggesting that both compounds are governed by the same antiferromagnetic quantum criticality. The resemblance of the doping effect on the SC order among Ni-, Sn-, and Pt-substituted CeCoIn 5 supports the argument that the doped carriers are primarily responsible for the breakdown of the SC order. The present investigation further reveals the quantitative differences in the trends of the suppression of superconductivity between Ce(Co,Ni)In 5 and the other alloys, such as the rates of decrease in T c , dT c /dx, and specific heat jump at T c , d(∆C p /T c )/dx. We suggest that the occupied positions of the doped ions play an important role in the origin of these differences.

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“…The curves are very steep with average slopes -dH c2 /dT| T c =2.31 T/K. Taking T c =22 K and using Werthamer-Helfand-Hohenberg (WHH) formula [11] H c2 =-0.69(dH c2 /dT)| T c T c , the value of upper critical field was estimated to be H WHH c2 (0)=35 T, similar with LaFeAsO system [12]. Note that some recent results reported that the H c2 (T) no longer follows the WHH law at low temperatures in iron-based superconductors [13].…”

Section: Resultsmentioning

confidence: 99%

Superconducting Properties of Polycrystalline Ba₂Ti₂Fe₂As₄O

Sun¹,

Ablimit²,

Feng³

et al. 2014

Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013)

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A new superconductor Ba 2 Ti 2 Fe 2 As 4 O has been studied through electrical resistivity, magnetoresistance, magnetic susceptibility, Hall coefficient, Seebeck coefficient and specific heat measurements. Electrical resistivity shows that superconducting transition occurs at ∼22 K. A specific-heat jump ∆C≈300 mJ/mol K corresponding to superconducting transition was also observed. Further, magnetic susceptibility under low field indicates bulk superconductivity of this compound with shielding volume fraction 90%. Magnetoresistance under various magnetic fields gives an upper critical field H c2 (0)∼35 T and a coherence length ξ GL (0)∼31 Å. The negative value of Hall coefficient and Seebeck coefficient indicate that electron carriers are dominant, consistent with the result of theoretical calculation, which suggests that electrons transfer from Ti to Fe.

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Temperature and Purity Dependence of the Superconducting Critical Field,Hc2. III. Electron Spin and Spin-Orbit Effects

Cited by 3,192 publications

References 16 publications

Strongly linked current flow in polycrystalline forms of the superconductor MgB2

Strongly linked current flow in polycrystalline forms of the superconductor MgB2

Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo₁₋_xNi_xIn₅

Superconducting Properties of Polycrystalline Ba₂Ti₂Fe₂As₄O

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Temperature and Purity Dependence of the Superconducting Critical Field,Hc2. III. Electron Spin and Spin-Orbit Effects

Cited by 3,192 publications

References 16 publications

Strongly linked current flow in polycrystalline forms of the superconductor MgB2

Strongly linked current flow in polycrystalline forms of the superconductor MgB2

Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo1−xNixIn5

Superconducting Properties of Polycrystalline Ba2Ti2Fe2As4O

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Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo₁₋_xNi_xIn₅

Superconducting Properties of Polycrystalline Ba₂Ti₂Fe₂As₄O