Investigations of Magnetic Properties of Oleic Acid and Oleyl Amine Capped Nanostructured CoxNi1−x (0.2 ≤ x ≤ 0.8) Alloys

In this study, nanocrystalline oleic acid and oleyl amine capped Co x Ni1−x alloys (x = 0.2, 0.4, 0.6, 0.8) have been synthesized via chemical reduction route. As-prepared as well as annealed samples were characterized using FTIR spectroscopy, X-ray diffraction and transmission electron microscopy. CoNi alloys were found to be capped with oleic acid-oleylamine complex even after heat treatment up to 400 °BC. XRD patterns confirm that the CoNi alloys crystallize in pure fcc phase with average crystallite sizes in the range of 8–11 nm. TEM micrographs confirm nearly spherical morphologies with narrow particle size distribution of the synthesized CoNi alloys. Average TEM particle sizes range from 7 nm to 12 nm. As-prepared as well as annealed CoNi alloys are ferromagnetic in nature at 298 K. M s values for annealed CoNi alloys are found to be in the range of 25–59.6 emu/g after correction for weight fraction of capped matrix and H c values are in the range of 52–314 Oe. Observed magnetic properties have been interpreted on the basis of size effects, altered crystal anisotropies and spin canting on the surface. FC/ZFC magnetization measurements show magnetic irreversibility and superparamagnetic blocking of nanoparticles due to strong dipolar interactions and particle size distribution. A structure-property correlation in CoNi alloys has been attempted in this investigation.