Effect of Cr-doping on dielectric, electric and magnetic properties of Zn0.96Cu0.04O nanopowders

Abstract

Cr doped Zn0.96Cu0.04O nanopowders with different Cr concentrations from 0% to 4% were successfully synthesized by a simple co-precipitation method. X-ray diffraction patterns revealed that all the samples had hexagonal crystal structure and co-doping could not alter its hexagonal structure. The dielectric dispersion and dielectric loss were increased with Cr concentrations due to the increase of charge carrier density, dipoles and vacancies within the grains. At higher frequency, the dielectric loss was found to be low because of the inhibition of domain wall motion. The low dielectric constant and dielectric loss at high frequency region makes it to be a suitable material for high frequency applications. The conductivity was increased by Cr-doping due to the enhanced transition of charge carriers between the grains. The strong suppression of ultraviolet emission at higher Cr revealed the promotion of non-radiative recombination. A broad defect-related visible luminescence band gave evidence for an increase in optically active deep level defects with increased Cr doping level. The combined effect of intrinsic defects and exchange interactions involving Cr ions substituted for Zn in the Zn-Cu-O lattice were responsible for the observed room temperature ferromagnetism. The saturation magnetization of the Cu doped ZnO was decreased by Cr co-doping, which occurred due to the antiferromagnetic coupling of neighboring Cu-Cu ions and Cr-Cr ions. The segregation of spinel ZnCr2O4 phase is responsible for the enhanced coercivity at higher Cr concentration (4%).