Reversibility in superconducting granular NiBi₃ embedded in a Bi matrix

NiBi₃ grains embedded in a Bi matrix are investigated with the aim of demonstrating superconducting reversibility within the precision limits of the measurements. The samples were prepared by co-depositing Ni and Bi in varying proportions, denoted as Bi(100-x)Ni(x) with x = 0, 1, 2, 3, 4, 5, and 10, ensuring the complete reaction and consumption of Ni. Phase composition and microstructural characteristics were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrical transport and magnetic properties were measured using a Quantum Design Dynacool Physical Property Measurement System (PPMS). The nucleation and density of NiBi₃ grains in the Bi(100-x)Ni(x) samples were found to increase progressively with increasing Ni content (x), from 1% to 10%. The study explores the influence of Ni composition on superconducting properties, including critical temperature, magnetoresistive transition behavior, and the amplitude of the diamagnetic signal associated with the superconducting phase. The observed reversibility is consistent with Ekin’s criteria and is attributed to the encapsulation of NiBi₃ grains by a superconducting Bi layer.