Magnetic properties of magnetically soft nanocomposite Co-SiO/sub 2/ prepared via mechanical milling

Nanocomposite of Co-SiO/sub 2/, a soft magnetic material, with Co weight fraction x = 0.3 and 0.7 was prepared via mechanical milling. The magnetic properties of these samples, both zero-field-cooled (ZFC) and field-cooled (FC), have been measured as a function of x, milling time, and temperature. The structural assessment of the composite indicates a presence of only ferromagnetic hcp/fcc-Co phase in the composite. However, reported magnetic properties of these composites appear to be dependent on the presence of antiferromagnetic phases of cobalt oxide as well. The FC magnetic measurements show a presence of an exchange bias field and an enhanced coercivity which are higher than the ZFC measurements. All magnetic measurements indicate that the overall magnetic properties of the composite are dictated by the presence of a trace amount of cobalt oxides which remain undetected in XRD.