Surface defect mediated magnetic interactions and ferromagnetism in Cr/Co Co-doped ZnO nanoparticles

► Nanoparticles Zn0.97−xCrxCo0.03O (x=0.0, 0.03, 0.06 and 0.09) are synthesized through sol-gel route. ► Crystalline structure and single phase character are confirmed by XRD, SEM, TEM, SAED and EDAX techniques. ► Raman and UV-vis spectra reveal the incorporation of Cr and Co into the ZnO lattice structure. ► The oxygen vacancies are observed from XPS and Raman spectra but there is no evidence of Co metallic cluster or CoO. ► The observed ferromagnetism is intrinsic in nature and not due to any metallic Co segregation or cobalt oxide which can be explained by bound magnetic polaron (BMP) theory.