Structural and magnetic properties of superconductor NiBi3/α-Bi2O3 synthesized by mechanical alloying.

A nanostructured NiBi3/α-Bi2O3 superconductor composite has been synthesized by the process of mechanical alloying through 19 h of high energy ball milling. The kinetics of formation is analyzed in detail by x-ray diffraction and the Rietveld method. A simple method is proposed to determine the crystallinity of the resulting sample by using the background Rietveld fitting that permits a quantitative analysis of the diffuse x-ray profile taking into account the air and Compton scattering. The diffuse scattering is attributed to the formation of a nanocluster of α-Bi2O3 which is confirmed by high-resolution transmission electron microscopy and Raman measurements. The magnetic measurements show superconducting transition at around 4 K and the existence of NiBi3/α-Bi2O3 nanophases with a low irreversibility field at around 1.01 T at 2 K. Analysis of magnetic susceptibility and isothermal magnetic hysteresis of the NiBi3/α-Bi2O3 nanocomposite indicates the simultaneous existence of bulk superconductivity and ferromagnetism below 4 K. [ABSTRACT FROM AUTHOR]