Publication Date

2-1-2018

Department

Ames Laboratory; Physics and Astronomy; Materials Science and Engineering

Campus Units

Materials Science and Engineering, Physics and Astronomy, Ames Laboratory

OSTI ID+

1421577

Report Number

IS-J 9358

DOI

10.1103/PhysRevB.97.054511

Journal Title

Physical Review B

Volume Number

97

Issue Number

5

First Page

054511

Abstract

We present a thorough study of doping dependent magnetic hysteresis and relaxation characteristics in single crystals of ( B a 1 − x K x ) F e 2 A s 2 ( 0.18 ≤ x ≤ 1 ). The critical current density J c reaches maximum in the underdoped sample x = 0.26 and then decreases in the optimally doped and overdoped samples. Meanwhile, the magnetic relaxation rate S rapidly increases and the flux creep activation barrier U 0 sharply decreases in the overdoped sample x = 0.70 . These results suggest that vortex pinning is very strong in the underdoped regime, but it is greatly reduced in the optimally doped and overdoped regime. Transmission electron microscope (TEM) measurements reveal the existence of dislocations and inclusions in all three studied samples x = 0.38 , 0.46, and 0.65. An investigation of the paramagnetic Meissner effect (PME) suggests that spatial variations in T c become small in the samples x = 0.43 and 0.46, slightly above the optimal doping levels. Our results support that two types of pinning sources dominate the ( B a 1 − x K x ) F e 2 A s 2 crystals: (i) strong δl pinning, which results from the fluctuations in the mean free path l and δ T c pinning from the spatial variations in T c in the underdoped regime, and (ii) weak δ T c pinning in the optimally doped and overdoped regime.

DOE Contract Number(s)

AC02-07CH11358

Language

en

Department of Energy Subject Categories

36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Publisher

Iowa State University Digital Repository, Ames IA (United States)

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