Granular behavior observed in the polycrystalline superconducting LiFeAs

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 (T_c) 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 [H_c2(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. (paper)