Physical property and electronic structure characterization of bulk superconductingBi3Ni

Abstract

We report the experimental and theoretical study of the magnetic nature of theBi3Ni system. The structure is found to be orthorhombic (Pnma) with latticeparameters a = 8.879 Å, b = 4.0998 Å and c = 4.099 Å. The title compound is synthesized via a solid state reaction route by quartzvacuum encapsulation of 5 N purity stoichiometric ingredients of Ni and Bi. Thesuperconducting transition temperature is found to be 4.1 K as confirmedfrom magnetization and specific heat measurements. The lower critical field(Hc1) and irreversibilityfield (Hirr) are around 150 and 3000 Oe respectively at 2 K. Upper critical field (Hc2), as determined from in-field (up to 4 T) ac susceptibility, is found to be around 2 T at 2 K.The normal state specific heat is fitted using the Sommerfeld–Debye equationC(T) = γT + βT3 + δT5 and the parametersobtained are γ = 11.08 mJ mol − 1 K − 2, β = 3.73 mJ mol − 1 K − 4 and δ = 0.0140 mJ mol − 1 K − 6. The calculated electronic density of states (DOS) at the Fermi levelN(EF) and Debyetemperature ΘD are 4.697 states/eV/f.u. and 127.7 K respectively. We also estimated the value of the electron–phonon coupling constant(λ) to be 1.23, which when substituted in the MacMillan equation givesTc = 4.5 K. Density functional theory (DFT) based calculations for experimentallydetermined lattice parameters show that Ni in this compound is non-magneticand ferromagnetic interactions seem to play no role. The Stoner conditionIN(EF) = 0.136 per Ni atom also indicates that the system cannot have any ferromagnetism. The fixed spinmoment (FSM) calculations, by fixing total magnetic moment on the unit cell, alsosuggested that this system does not exhibit any signatures of ferromagnetism.