Control of defects and magnetic properties in colloidal HfO2 nanorods

Colloidal HfO2 nanorods with controllable defects are synthesized. An increased defect concentration is observed by high-resolution electron microscopy and by optical absorption spectroscopy. Nanocrystals with a high defect concentration exhibit ferromagnetism and superparamagnetic-like behavior (see figure). This low-temperature colloidal syntheses can produce the highly nonequilibrium defect concentrations needed to obtain ferromagnetism in closed shell oxides.