Microwave absorption study of pinning regimes in Ba(Fe_1−xCo_x)₂As₂ single crystals

Abstract

Magnetic field dependent modulated microwave absorption (MMWA) measurements have been carried out to investigate vortex pinning effects in single crystals of the iron-based high-Tc superconductor Ba(Fe1−xCox)2As2 with three different cobalt doping levels of x = 0.07, 0.09, and 0.11. The dependence of the MMWA hysteresis loops on temperature, magnetic field, and Co-concentration have been measured and analyzed using a theoretical model of microwave absorption in superconductors. The analysis reveals that in an underdoped crystal (x = 0.07) the so called δTc-pinning due to magnetically ordered regions defines the temperature dependence of the critical current density, while in the optimally doped (x = 0.09) and overdoped (x = 0.11) samples the pinning is governed by structural imperfections due to inhomogeneous distribution of cobalt dopant and has the so called δl character.

Observation of a Structure and Line Shape Evolution of Non-resonant Microwave Absorption in a SmFeAs(O, F) Polycrystalline Iron Pnictide Superconductor

“…Therefore, NRMA studies in iron pnictide superconductors are important. So far, high field sweep magnetically modulated microwave absorption (MMMA) studies have been reported in iron pnictide superconductors [12, 36,37], but at low field sweep, the microwave absorption is unclear. Here, we report a systematic study of low field sweep NRMA on SmFeAsO 0.88 F 0.12 polycrystalline as a function of temperature and field modulation amplitude.…”