Upper critical and irreversibility fields in Ni- and Co-doped pnictide bulk superconductors

作者：Nikolo Martin; Singleton John; Solenov Dmitry; Jiang Jianyi; Weiss Jeremy; Hellstrom Eric

来源：Physica B: Condensed Matter , 2018, 536: 833-838.

DOI：10.1016/j.physb.2017.09.047

• Superconductivity
• Pnictides
• Upper critical magnetic field
• Irreversibility field

A comprehensive study of upper critical and irreversibility magnetic fields in Ba(Fe0.95Ni0.05)(2)As-2 (large grain and small grain samples), Ba(Fe0.94Ni0.06)(2)As-2, Ba(Fe0.92Co0.08)(2)As-2, and Ba(Fe0.92Co0.09)(2)As-2 polycrystalline bulk pnictide superconductors was made in pulsed fields of up to 65 T. The full magnetic field-temperature (H-T) phase diagrams, starting at 1.5 K, were measured. The higher temperature, upper critical field H-c2 data are well described by the one-band Werthamer, Helfand, and Hohenberg (WHH) model. At low temperatures, the experimental data depart from the fitted WHH curves, suggesting an emergence of a new phase that could be attributed to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The large values of the Maki fitting parameter a indicate that the Zeeman pair breaking dominates over the orbital pair breaking and spin-paramagnetic pair-breaking effect is significant in these materials. Possible multi-band structure of these materials is lumped into effective parameters of the single-band model. Table of measured physical parameters allows us to compare these pnictide superconductors for different Co- and Ni- doping levels and granularity.

• 出版日期2018-5-1
• 单位Los Alamos