Effects of Al_2O_3 Nanoparticle on the Microstructure and Magnetic Properties of Co/ Al_2O_3 Coatings Prepared by Composite Plating

摘要

Nanocomposite Co/ Al_2O_3 coatings were fabricated by composite electrodeposition. The nanosized Al_2O_3 particles were suspended in aqueous cobalt sulfamate solution and subsequently co-deposited on a Cu substrate. The samples were characterized by Scanning electron microscopy and Atomic force microscopy for determination of surface morphology. X-ray diffraction technique concomitant with Transmission electron microscopy were utilized to identify the phases and emanation of microstructure while magnetic properties of the Co/ Al_2O_3 nanocomposite coatings were investigated by vibrating sample magnetometer. The results indicated that, the Al_2O_3 nanoparticles suspended in the plating solution acquired a positively charge due to the presence of Co ions. These positively charged Al_2O_3 particles drift towards the cathode by electrophoresis and are reduced by Co ions to form the Co/ Al_2O_3 composite film. The Co grains in the films show hcp structure with (11 20) preferred orientation. The grain size and surface roughness of the Co/ Al_2O_3 compositesis found to decrease with increasing Al_2O_3 volume fraction while the magnetization of the composite films decreases with increasing concentration of Al_2O_3 nanoparticles. However the coercivity of the coatings was found to increase with increasing Al_2O_3 content. It could be delineated from the TEM micrographs that the Al_2O_3 nanoparticles dispersed in the Co matrix inhibited the grain growth of Co matrix resulting in pinning of the magnetic domains due to which the coercivity of the composite layers was found to increase.