Structure, optical and ferromagnetic properties of Zn 1−x−y Mn x Cr y O nanoparticles diluted magnetic semiconductors synthesized by citrate sol–gel method

Citrate sol–gel method has been employed for synthesis of Zn1˗x˗yMnxCryO nanomaterials. Binary Zn0.9Mn0.1O and Zn0.9Cr0.1O nanomaterials were prepared and their optical and magnetic properties were investigated as reference compositions for the individual behavior of both of Mn- and Cr doping, respectively. The synthesized nanoparticles were analyzed using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), ultraviolet–visible (UV–Vis) spectroscopy and vibrating sample magnetometer. For low Mn–Cr-codoping contents, i.e., 2 and 4%, XRD revealed formation of single-phase ZnO nanoparticles in the wurtzite type hexagonal lattice, whereas 10% doping concentration, either Mn- or Cr-single doping or codoping, resulted in formation of wurtzite ZnO as a major phase with ZnMnO3 or/and ZnCr2O4 secondary phases. From XRD and HRTEM, the produced nanomaterials have average crystallite sizes ranged from 15 to 35 nm. Applying Kubelka–Munk function, optical band gap energy (Eopt) was determined. Eopt of single Mn- and Cr-doped ZnO increased than that of bulk ZnO mainly due to Burstein–Moss effect, whereas it decreased in the codoped Zn1−x−yMnxCryO because of the negative and positive corrections in the conduction and valence band, respectively, brought about by alteration of the sp–d exchange interactions between the band electrons and the localized d-electrons of the Mn2+ and Cr3+ ions. Magnetization measurements indicated that Cr induced the paramagnetism, while Mn induced the RT ferromagnetism in the synthesized Zn1−x−yMnxCryO nanoparticles. The ferromagnetic Zn1−x−yMnxCryO compositions could be potential candidates for Mn–Cr-codoped ZnO-based DMS nanoparticles.