Ferromagnetic behavior of high-purity ZnO nanoparticles

► ZnO nanoparticles with wurtzite structure were prepared at low temperature. ► Magnetization versus temperature and isothermal measurements, M(H), were obtained. ► The nanoparticles present a core-shell structure. ► The coercive field shows ferromagnetism above room temperature. ► Oxygen vacancies are the main factors for the ferromagnetic behavior.