Enhancement of room temperature ferromagnetic behavior of Co-doped ZnO nanoparticles synthesized via sol–gel technique

Zn1−xCoxO (x = 0, 0.001, 0.005, 0.01, 0.02, 0.04, and 0.06) nanoparticles (NPs) were synthesized by sol–gel method. Ingestion of Co2+ ions in the ZnO crystal lattice created defects without disturbing the original crystal structure of ZnO. This is confirmed by the X-ray diffraction (XRD) studies and is also observed in the photoluminescence (PL) emission study where the Co-doped ZnO NPs have shown emissions in the green and yellow-orange regions of visible spectrum. XRD and transmission electron microscopic (TEM) analysis showed reduction in crystallite size from 29 to 14.5 nm and from 51 to 36 nm, respectively, with increase in Co2+ ions concentration. Optical absorption spectroscopic studies (UV-visible spectroscopy) of these samples show significant peak shift towards higher energy (blue shift), which is in accordance with the Kubo’s theory. Magnetic properties were studied using quantum designed vibrating sample magnetometry (VSM), which confirmed that Co-doped ZnO NPs exhibit room temperature ferromagnetism (RTFM) for the samples having high Co concentration. With these notable properties, this study suggests that Co-doped ZnO NPs may be useful in the field of optoelectronic devices and memory-storage devices as well.