Signatures of filamentary superconductivity in antiferromagnetic BaFe₂As₂ single crystals

¹ Blackett Laboratory, Imperial College - London, SW7 2AZ, UK
² Oak Ridge National Laboratory - Oak Ridge, TN 37831, USA
³ Department of Materials Science and Engineering, University of Tennessee - Knoxville, TN 37996, USA
⁴ Instituto de Física, Universidade Federal do Rio de Janeiro - Rio de Janeiro, RJ 21941-972, Brazil

^(a) l.cohen@imperial.ac.uk

Received: 20 April 2015
Accepted: 27 July 2015

Abstract

In this paper, we present ac susceptibility and magnetotransport measurements on aged single crystals of the ferropnictide parent compound, BaFe₂As₂ with a paramagnetic-to-antiferromagnetic transition temperature of 134 K. The ac susceptibility shows the clear onset of a partial diamagnetic response with an onset temperature, commensurate with a subtle downturn in resistivity at approximately 20 K. Below 20 K the magnetotransport shows in-plane anisotropy, magnetic-field history dependence and a hysteretic signature. Above 20 K the crystals show the widely reported high-field linear magnetoresistance. An enhanced noise signature in ac susceptibility is observed above 20 K, which varies in character with amplitude and frequency of the ac signal. The hysteresis in magnetoresistance and the observed sensitivity of the superconducting phase to the amplitude of the ac signal are indicative characteristics of granular or weakly linked filamentary superconductivity. These features taken together with the observed noise signature above suggests a link between the formation of the superconducting filamentary phase and the freezing of antiphase domain walls, known to exist in these materials.