Structure, magnetic properties, and thermal stability of chemically prepared nickel carbide nanoparticles

Single phase nickel carbide nanoparticles and phase separated nickel carbide/elemental nickel nanocomposites have been prepared by the reduction of nickel acetate in triethylene glycol at reduction temperatures between 250 and 290 ^○C. The structure, magnetic properties, and thermal stability of these samples have been studied by x-ray diffraction (XRD), vibrating sample magnetometry (VSM), and differential scanning calorimetry (DSC) measurements. The XRD measurements indicate that the nickel carbide phase is hexagonal (S.G. 167) with lattice parameters of a=0.45908(1) and c=1.30080(3) nm; somewhat larger values than previously reported. The hexagonal phase has a room temperature magnetization of about 0.2 emu/g and a Curie temperature of about 330 ^○C. At a heating rate of 10 ^○C/min the hexagonal phase irreversible transforms to face-center-cubic elemental nickel starting at a temperature of about 380 ^○C.