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Strong pinning and slow flux creep relaxation in Co-doped CaFe2As2 single crystals
Solid State Communications ( IF 2.1 ) Pub Date : 2020-09-01 , DOI: 10.1016/j.ssc.2020.113963
N. Haberkorn , S. Suárez , S.L. Bud'ko , P.C. Canfield

Abstract 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.

中文翻译:

Co掺杂CaFe2As2单晶中的强钉扎和缓慢的通量蠕变弛豫

摘要 我们通过磁化测量报告了 Tc ≈ 15.7 K 的独立 Ca(Fe1−xCox)2As2 (x ≈ 0.033) 单晶的临界电流密度 Jc 和磁通蠕变速率 S 的测量结果。Jc 在低温下的磁场依赖性显示出与强钉扎相关的特征。此外,我们发现该系统显示出较小的通量蠕变率。原始晶体的特征玻璃指数 μ 和钉扎能 U0 显示出异常高的值。我们发现对于 0.3 T 和 1 T 之间的磁场,μ 从 ≈ 2.8 减小到 ≈ 2 并且 U0 保持 ≈ 300 K。钉扎力的分析表明该机制类似于在多晶系统中观察到的机制,其中晶界和随机无序产生涡旋钉扎。考虑到在单晶中观察到的大 U0,我们试图通过 2 × 1016 质子/cm2 的能量密度的 3 MeV 质子辐照添加随机点无序来改善钉扎。结果表明,与其他铁基超导体不同,超导部分因辐照而急剧降低。这一事实表明,系统中的超导性对于无序的增加极其脆弱。通过热退火去除无序后,被照射晶体中的超导体积分数系统地恢复,这证明了在磁化与磁场曲线中观察到临界状态。对于辐照样品,没有观察到与重入反铁磁跃迁相关的特征。结果表明,与其他铁基超导体不同,超导部分因辐照而急剧降低。这一事实表明,系统中的超导性对于无序的增加极其脆弱。通过热退火去除无序后,被照射晶体中的超导体积分数系统地恢复,这证明了在磁化与磁场曲线中观察到临界状态。对于辐照样品,没有观察到与重入反铁磁跃迁相关的特征。结果表明,与其他铁基超导体不同,超导部分因辐照而急剧降低。这一事实表明,系统中的超导性对于无序的增加极其脆弱。通过热退火去除无序后,被照射晶体中的超导体积分数系统地恢复,这证明了在磁化与磁场曲线中观察到临界状态。对于辐照样品,没有观察到与重入反铁磁跃迁相关的特征。通过热退火去除无序后,被照射晶体中的超导体积分数系统地恢复,这证明了在磁化与磁场曲线中观察到临界状态。对于辐照样品,没有观察到与重入反铁磁跃迁相关的特征。通过热退火去除无序后,被照射晶体中的超导体积分数系统地恢复,这证明了在磁化与磁场曲线中观察到临界状态。对于辐照样品,没有观察到与重入反铁磁跃迁相关的特征。
更新日期:2020-09-01
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