Size dependent ferromagnetism in dodecyl amine capped ZnO nanoparticles

Highlights: • ZnO nanoparticles at different sizes were prepared using solution phase synthesis technique. • Nanoparticles have been shown to be compressively strained with reduced particle size. • The size dependent strain is shown to give rise to concomitant shifts in the elemental binding energies in zinc oxide (ZnO) nano particles. • Ferromagnetism ZnO was shown to be considerably enhanced with particles size reduction. • The size dependent ferromagnetism strongly depends on the oxygen defect state and PL behaviour. -- Abstract: We investigated the size dependent ferromagnetism in dodecyl amine capped zinc oxide nanoparticle. X-ray diffraction and X-ray photoelectron spectroscopy analysis demonstrated that density of oxygen vacancies was enhanced due to an increase in compressive strain concomitant with the decrease in particle size. Magnetic measurements showed increased ferromagnetic ordering in ZnO nanoparticles with reduced particle size. It was also found that the increase in coercive field, saturation magnetization and magnetic hysteresis loop area were invariably associated with increased oxygen defect population. The observed ferromagnetism in organic capped zinc oxide nanocrystals has therefore been assigned to defect induced phenomena. Results of sample characterization using optical absorption spectroscopy, photo luminescence spectroscopy and high resolution transmission electron microscope have also been presented