Physical property and electronic structure characterization of bulk superconducting Bi3Ni

Abstract

We report the experimental and theoretical study on magnetic nature of Bi3Ni system. The structure is found to be orthorhombic (Pnma) with lattice parameters a = 8.879{\AA} b = 4.0998{\AA} and c = 4.099{\AA}. The title compound is synthesized via a solid state reaction route by quartz vacuum encapsulation of 5N purity stoichiometric ingredients of Ni and Bi. The superconducting transition temperature is found to be 4.1 K as confirmed from magnetization and specific heat measurements. The lower critical field (Hc1) and irreversibility field (Hirr) are around 150 and 3000Oe respectively at 2K. Upper critical field (Hc2) as determined from in field (up to 4 Tesla) ac susceptibility is found to be around 2 Tesla at 2K. The normal state specific heat is fitted using Sommerfeld-Debye equation C(T) = {\gamma}T + {\beta}T3+{\delta}T5 and the parameters obtained are {\gamma}= 11.08mJ/mol-K2, {\beta}= 3.73mJ/mol-K4 and {\delta}= 0.0140mJ/mol-K6. The calculated electronic density of states (DOS) at Fermi level N(EF) and Debye temperature {\Theta}D are 4.697 states/eV per formula unit and 127.7K respectively. We also estimated the value of electron phonon coupling constant ({\lambda}) to be 1.23, which when substituted in MacMillan equation gives Tc = 4.5K. Density functional (DFT) based calculations for experimentally determined lattice parameters show that Ni in this compound is non-magnetic and ferromagnetic interactions seem to play no role. The Stoner condition I*N(EF) = 0.136 per Ni atom also indicates that system cannot have any ferromagnetism. The fixed spin moment (FSM) calculations by fixing total magnetic moment on the unit cell also suggested that this system does not exhibit any signatures of ferromagnetism.