Room temperature ferromagnetism and photoluminescence of nanocrystalline Zn1 − xCoxO thin films prepared by sol–gel MOD

Abstract

Zn1 − xCoxO (ZC) [x = 0, 1, 3, 5, 7 and 9 mol%] thin films were prepared by sol–gel combined metallo-organic decomposition method. The films were deposited on the Si substrate with spin-coating technique and annealed at 600 °C for 3 h. X-ray diffraction pattern shows the formation hexagonal wurtzite phase and distortion (c/a) decreases with increasing Co concentration in ZnO. The average grain size is measured using Scherer relation. Atomic force microscopy is used to confirm the formation of nanograins resulted by the use of polyethylene glycol as surfactant. The photoluminescence was recorded by using He-Cd laser of excitation wavelength 325 nm in wavelength region of 350–650 nm which exhibits some influence of Co doping on the multiplication of defects such as O vacancies, Zn interstitials and grain boundary defects. All thin films show room temperature ferromagnetism except pure ZnO which is diamagnetic and 9 mol% of Co shows paramagnetism. This behaviour is interpreted as due to fluctuations in the magnetic ordering, depending on grain size and site location in grain boundaries or oxygen vacancies.