Mn-doped ZnO nanocrystalline thin films prepared by ultrasonic spray pyrolysis

Zn1−xMnxO (x = 0.03, 0.05, 0.07 and 0.10) thin films were synthesized by low cost ultrasonic spray pyrolysis technique on simple glass substrate at low substrate temperature. The films were characterized by X-ray diffraction (XRD), UV–vis spectrometer and superconducting quantum interference device magnetometer (SQUID). The influence of doping concentration on structural, optical and magnetic properties of the films was studied in detail. Structural and optical properties of the films elucidated that the Mn2+ ions have substituted the Zn2+ ion without changing the wurtzite structure of ZnO. No impurity phase was observed in XRD pattern even after doping 10 at.% of Mn. The value of band gap was found to decrease from 3.24 eV to 3.14 eV with corresponding increase in Mn concentration from x = 0.03 to 0.10. The observed decrease in the band gap with increase in doping concentration was explained in terms of a sp–d exchange interaction. A non-linear M–H behavior observed at 5 K indicate weak ferrimagnetic behavior at low temperature. The value of coercivity and the remanant magnetization at 5 K for 7 at.% Mn-doped films was observed to be 147 Oe, and 3.77 × 10−5 emu, respectively. However there was no indication of room temperature ferromagnetism in these films. The concave nature of M(T) behavior with steep rise of magnetization was observed at low temperature and was explained in terms of polaron-percolation-theory.