Intrinsic magnetism in Zn1−xCoxO (0.03≤x≤0.10) thin films prepared by ultrasonic spray pyrolysis

Abstract

The Zn1−xCoxO thin films were prepared on a commercial glass substrate at400 °C by ultrasonic spray pyrolysis. The effect of doping concentration on thestructural, optical and magnetic properties of these films has been studied.The structural and optical properties of these films reflect the fact that theCo2+ ions havesubstituted the Zn2+ ions without changing the wurtzite structure of ZnO. We have not observed any secondaryphases even after doping the 10 at.% concentration of Co. All the films were highly orientedwith preferred (002) direction. By increasing the Co content, a systematic change in both thec-axis lattice constant and the fundamental band gap energy was observed. Threeabsorption bands were found in the transmission spectra of the Co doped ZnO films at657 nm (1.89 eV), 610 nm (2.03 eV) and 567 nm (2.20 eV). The absorption bands wereattributed to d–d intraionic transitions of tetrahedrally coordinated high-spinCo2+ ions. Magnetic studies reveal the absence of room temperatureferromagnetic behaviour in these films. The values of coercivity(HC)∼145 and 123 Oe andremanent magnetization (Mr)∼4.32 × 10−5 and 7.28 emu cm−2 wereobserved at 5 K for Zn0.95Co0.05O and Zn0.93Co0.07O thin films.