Room temperature ferromagnetism in CoO nanoparticles obtained from sonochemicallysynthesized precursors

Abstract

In this paper we report the magnetic properties of nanosized CoO particles, prepared fromsonochemically synthesized precursors and characterized using x-ray diffraction (XRD),conventional transmission electron microscopy (TEM) and scanning tunneling electronmicroscopy combined with energy dispersive x-ray analysis (STEM-EDX) techniques. Thenanoparticles were faceted and the sizes varied between 30 and 60 nm depending on thetime of annealing. They were stable even in the absence of any organic coating on them.Magnetic measurements reveal the presence of ferromagnetic interactions at lowtemperatures in the CoO nanoparticles synthesized after 2 and 4 h of annealing of thesonochemically synthesized precursor under nitrogen. However, after 6 h of annealing, thenanoparticles show hysteresis not only at low temperatures (1.5 K) but also at highertemperatures (100 K and room temperature), indicating the presence of room temperatureferromagnetism.