LAUSR

Abstract We have investigated CoPt nanoparticles by the simultaneous reduction of Pt (acac)2 and Co (acac)2 with polyol method under N2 atmosphere. The formation of CoPt nanoparticles requires further study of possible increased Pt concentration and size effects on their structural and magnetic properties. We found that as-synthesized CoPt NPs exhibits a chemically disordered cubic phase in the compositions with an average crystalize size of 4.44 nm confirmed by X-ray diffraction (XRD) method and Rietveld refinement analyses. Uniformly distributed the average cluster size of CoPtx nanoparticles decreased from 13.7 nm to 7.6 nm with decreased Pt concentration from 2.3 to 0.5 which determined by scanning electron microscopy (SEM). Magnetic properties are characterized by vibrating sample magnetometer (VSM) for zero-field cooled (ZFC) and field cooled (FC) conditions between 5 and 300 K and applied field up to ±5 T. Magnetic results indicate that the Co rich CoPtx nanoparticles exhibit large coercive field up to 1358 Oe at 5 K and this value decrease with increasing temperature and Pt concentration for all samples. Due to a transition from ferromagnetic to a superparamagnetic phase with elevated temperature, coercivity and exchange bias nearly vanished for all samples.