Magnetic and structural properties of Co nanoparticles in a polymeric matrix

Magnetic, magnetic resonance and structural properties of Co nanoparticles in polyethylene matrix have been investigated. The materials were prepared by a method of thermal decomposition of cobalt formate in the polyethylene melt in a mineral oil and contained 4wt% of Co. Transmission electron microscopy data showed that the particles diameter was 4nm. According to EXAFS studies the particles can be presented as consisting of metallic core and a surface shell interacting with the surrounding matrix. Magnetic and magnetic resonance studies showed that the material has high blocking temperature (about 600K) and the magnetic anisotropy constant of the nanoparticles is of an order of magnitude higher than that in a bulk cobalt. The origin of the high magnetic anisotropy of the Co nanoparticles is related to the surface effects. The material has relatively high hysteresis at room temperature (590 Oe), which makes it promising for magnetic recording applications. (C) 2003 Elsevier Science B.V. All rights reserved.