Magnetic properties of CoO nanocrystals prepared with a controlled reaction atmosphere

Abstract

In this work CoO nanocrystals with a cubic crystal structure were prepared by the thermal decomposition of cobalt(II) acetate tetrahydrate in a mixture of oleylamine and oleic acid with a controlled reaction atmosphere. The particle size is controlled by the binding capability of the ligands which is affected by the presence or absence of oxygen. The magnetic properties of the CoO nanocrystals of different particle sizes were studied and compared. Large exchange bias was found for the smaller CoO nanoparticles (58 nm) prepared in the presence of oxygen due to uncompensated spins on the surface. The magnetic behavior for the larger nanocrystals (275 nm) is dominated by the spins associated with the defects inside the CoO nanoparticles.