Granular behavior observed in the polycrystalline superconducting LiFeAs

Abstract

Stoichiometric polycrystalline LiFeAs has been synthesized by a two-step solid state reaction method at low sintering temperature (600 °C) and its physical properties have been characterized. Room temperature x-ray diffraction confirms the phase purity of the samples, and microstructural analysis provides evidence that polycrystalline LiFeAs samples have a dense and nearly homogeneous microstructure with disk-shaped grains. Bulk superconductivity is established at the onset transition temperature (Tc) of 19.2 K. Both the onset and offset resistive transition temperatures shift to lower temperature in applied magnetic field (≤15 T) which yield an estimated upper critical field [Hc2(0)] at zero temperature of about 41 T. Two distinct scales of current flow corresponding to inter- and intragranular shielding currents are revealed by remanent magnetization measurements of bulk samples. The calculated intergranular current density at self-field and 5 K is ∼4.4 × 102 A cm−2. The analysis of the superconducting properties suggests evidence of weak-links and the electromagnetic granular nature of polycrystalline LiFeAs similar to other pnictide superconductors.