Physical property and electronic structure characterization of bulk superconducting Bi3Ni

We report the experimental and theoretical study of the magnetic nature of the Bi3Ni system. The structure is found to be orthorhombic (Pnma) with lattice parameters a = 8.879 angstrom, b = 4.0998 angstrom and c = 4.099 angstrom. The title compound is synthesized via a solid state reaction route by quartz vacuum encapsulation of 5 N 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 (H-c1) and irreversibility field (H-irr) are around 150 and 3000 Oe respectively at 2 K. Upper critical field (H-c2), 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 equation C(T) = gamma T + beta T-3 + delta T-5 and the parameters obtained are gamma = 11.08 mJ mol(-1) K-2, beta = 3.73 mJ mol(-1) K-4 and delta = 0.0140 mJ mol(-1) K-6. The calculated electronic density of states (DOS) at the Fermi level N(E-F) and Debye temperature Theta(D) are 4.697 states/eV/f.u. and 127.7 K respectively. We also estimated the value of the electron-phonon coupling constant (lambda) to be 1.23, which when substituted in the MacMillan equation gives T-c = 4.5 K. Density functional theory (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 IN(E-F) = 0.136 per Ni atom also indicates that the 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.