Defect-induced weak ferromagnetism in transition metal-doped ZnO nanoparticles

In this work, citric acid-capped and ethylene glycol-stabilized pristine and transition metal (TM = Co, Fe, Mn and Ni)-doped ZnO nanoparticles with the generic formula Zn1-xTMxO, x = 0.01 and 0.02, have been synthesized by sol-gel method. XRD confirmed the phase purity of all the samples. Average crystallite size calculated from Scherrer formula was within the range of 43 +/- 25 nm for different doped samples. The Raman spectra of (Co, Mn and Ni)-doped ZnO show strong E-2 (high) and E-1 (LO) modes. The synthesized samples also show strong luminescent emission from inherent Zn and O point defects (interstitial and vacancies) along with a sharp excitonic peak centred at 362 nm. Magnetic studies at 300 K reveal that all samples show weak room-temperature ferromagnetism at low magnetic fields with unsaturated M-H plot up to a measuring field of 5 T.