Optical and magnetic properties of laser-deposited Co-doped ZnO thin films

We report the optical and magnetic properties of laser-deposited Zn1−xCoxO (x=0.06–0.3) thin films with no intentional electrical carrier doping. The analysis of the high-temperature magnetization data provides an unambiguous evidence that antiferromagnetic superexchange interaction is the dominant mechanism of the exchange coupling between Co ions in Zn1−xCoxO alloy, yielding the value of the effective exchange integral J1/kB to be about −27 K. The low-temperature magnetization data reveals a spin glass transition in Zn1−xCoxO alloy for the Co content x>0.15, giving the value of the spin freezing temperature Tf to be ∼8 and ∼12 K for x=0.2 and 0.25, respectively. Optical spectra analysis shows a linear increase of the band gap Eg with the increase of the Co content following Eg=3.231+1.144x eV.