Chemical synthesis of Co/Cu core/shell nanocomposites and evaluation of their magnetic properties

Co/Cu core/shell nanocomposites (CSNCs) with varying shell thickness were synthesized through a modified polyol process in conjunction with a transmetallation reaction. Tuning of shell thickness was achieved by subtle change in concentration of copper acetate infused in different experiments against a fixed cobalt precursor concentration. Formation of Cu nanoparticles (NPs) was observed from UV–vis spectra, which showed a typical surface plasmon resonance peak at 560 nm. Precise control over particle size was obtained by the use of PVP as stabilizer, which was confirmed by a red shift of 20 cm−1 in the CO stretching frequency of various PVP coated Co/Cu CSNCs. Powder X-ray diffraction patterns elucidate the co-existence of distinctive fundamental peaks for both Co and Cu indicating that they have not formed an alloy during the reaction. TEM images corroborate with the above result by revealing the existence of lighter shaded Cu shells coated over dark inner cores of Co. Coalescence of adjacent Cu shells gives a matrix like appearance in case of Co21.2Cu78.8 NPs; whereas Co90.7Cu9.3 NPs were distinctly separated from each other. Magnetic hysteresis loops of all the Co/Cu CSNCs showed ferromagnetic behavior and an increase in magnetization value with decrease in shell thickness was observed.