Tailoring of room temperature ferromagnetism and electrical properties in ZnO by Co (3d) and Gd (4f) element co-doping

Nanoparticles of Co2+ and Gd3+ ions co-doped Zinc oxide were prepared by co-precipitation process followed by hydrothermal method. To obtain the desired crystallographic phase and also, to enhance the Oxygen vacancy, the as prepared sample was sintered at 400 °C in vaccum atmosphere. The presence of intrinsic defects and internal stress in the lattice structure of co-doped ZnO has been substantiated by the detail analysis of X-ray diffractograms. Different optical characterizations like Raman spectroscopy and photoluminescence (PL) spectra have been measured. The presence of defects/Oxygen vacancies are also critically analyzed by Raman and PL spectra of co-doped ZnO sample. Magnetic measurement such as magnetization as a function of magnetic field at different low temperatures (300-10 K) and magnetization as a function of temperature (field cooled and zero-field cooled) are measured by SQUID magnetometer. Interestingly, a very strong magnetic interaction and a large value of coercivity even at room temperature have been observed in the co-doped ZnO nanoparticles compared to the mono-doped ZnO nanoparticles. The presence of ferromagnetic ordering and large coercivity were successfully explained by the vacancy assisted bound-magnetic-polaron model and domain wall blowing theory. Negative exchange biased has been observed in our sample implies the formation and exchange interaction at the interface of FM/AFM bilayers. Dielectric measurement suggest that for both 5% Co2+ and Gd3+ ions co-doped ZnO system, the enhanced dielectric data is the contribution of large amount of space charge polarization and the intrinsic defects in the sample. Enhancement of the ac conductivity with the increase of temperature reveals the semiconducting nature of the co-doped ZnO systems.