Second magnetization peak, anomalous field penetration, and Josephson vortices in KCa2Fe4As4F2 bilayer pnictide superconductor
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We performed magnetization measurements in a single crystal of the anisotropic bilayer pnictide superconductor KCa2Fe4As4F2, with Tc≃ 34 K, for H‖c-axis and H‖ab-planes. A second magnetization peak (SMP) was observed in the isothermal M(H) curves measured below 16 K for H‖ab-planes. A peak in the temperature variation of the critical current density, Jc(T), at 16 K, strongly suggests the emergence of Josephson vortices at lower temperatures, which leads to the SMP in the sample. In addition, it is noticed that the appearance of Josephson vortices below 16 K renders easy magnetic flux penetration. A detailed vortex dynamics study suggests that the SMP can be explained in terms of elastic pinning to plastic pinning crossover. Furthermore, contrary to the common understanding, the temperature variation of the first peak field, H1, below and above 16 K, behaves non-monotonically. A highly disordered vortex phase, governed by plastic pinning, has been observed between 17 and 23 K, within a field region around an extremely large first peak field. Pinning force scaling suggests that the point defects are the dominant source of pinning for H‖ab-planes, whereas, for H ‖c-axis, point defects in addition to surface defects are at play. Such disorder contributes to the pinning due to the variation in charge carrier mean free path, δl -pinning. Moreover, the large Jc observed in our study is consistent with the literature, which advocates this material for high magnetic field applications.
Lopes , P V , Sundar , S , Salem-Sugui , S , Hong , W , Luo , H & Ghivelder , L 2022 , ' Second magnetization peak, anomalous field penetration, and Josephson vortices in KCa 2 Fe 4 As 4 F 2 bilayer pnictide superconductor ' , Scientific Reports , vol. 12 , 20359 . https://doi.org/10.1038/s41598-022-24012-z
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DescriptionFunding: PVL is supported by an MSc. grant from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). SS was supported by a post-doctoral fellowship from Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), project E-26/202.323/2021. LG was supported by FAPERJ, Projects E-26/010.001497/2019 and E-26/202.820/2018, and CNPq, project 308899/2021-0. This work is also supported by the National Key Research and Development Program of China (Grant No. 2018YFA0704200), the National Natural Science Foundation of China (Grants Nos. 11822411 and No. 11961160699), the Strategic Priority Research Program (B) of the CAS (Grants No. XDB25000000), the K. C. Wong Education Foundation (GJTD-2020-01), the Youth Innovation Promotion Association of CAS (Grant No. Y202001), the Postdoctoral Innovative Talent program(BX2021018) and the China Postdoctoral Science Foundation (2021M700250).
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