Magnetic properties of Co/(CoNi)Fe/sub 2/O/sub 4/ nanocomposite magnet powders

Co/(CoNi)Fe/sub 2/O/sub 4/ nanocomposite powders were prepared by mixing coprecipitated (CoO)/sub 0.9/(NiO)/sub 0.1//spl middot/Fe/sub 2/O/sub 3/ nanoparticles with Co nanoparticles, which were synthesized by alcohol reduction. TEM observations reveal that the powder consists of Co and (CoO)/sub 0.9/(NiO)/sub 0.1//spl middot/Fe/sub 2/O/sub 3/ nanoparticles with an average particle size of 30-50 nm. While the coercivity (H/sub cJ/) is 156 kA/m, the saturation magnetization (/spl sigma//sub s/) of 115.8 Am/sup 2//kg is obtained, which is comparable to that of Co nanoparticles. In the hysteresis loop, magnetization changes smoothly with field as the hysteresis behavior of a single-phase material. The high recoil ratio (R/sub recoil/) of 0.69 and the positive /spl Delta/M values suggest the presence of the exchange coupling between Co and (CoNi)Fe/sub 2/O/sub 4/ nanoparticles.