Synthesis and magnetic properties of CoO nanoparticles

Pure CoO nanoparticles in the 4.5-18 nm range have been prepared by the decomposition of Co(II) cupferronate in Decalin at 270 degrees C under solvothermal conditions. The particles have been characterized by X-ray diffraction, transmission electron microscopy, and cognate techniques. The particles are stable because of the organic coating that occurs in situ. The organic coating is readily removed by heating the particles to 260 degrees C without loss of the nanoparticulate nature. Magnetic measurements reveal the presence of ferromagnetic interactions at low temperatures in the small CoO nanoparticles (< 16 nm). The small nanoparticles do not exhibit a distinct antiferromagnetic transition around 300 K as the bulk sample but instead show hysteresis below a blocking temperature of similar to 10 K.