Enhancement of room-temperature ferromagnetism and dielectric response in nanocrystalline ZnO co-doped with Co and Cu

Enhancement of ferromagnetic ordering and dielectric response in the nanoparticles of Co and Cu co-doped ZnO are the most important findings presented in this report. The co-doped nanoparticles of ZnO were prepared by hydrothermal method. Hydrothermal synthesis is an important preparation technique to establish one dimensional growth of the nanoparticles along the easy axis and this technique on the other hand improves the defect densities in the doped ZnO systems. XRD analysis of the undoped and co-doped ZnO nanoparticles confirms the presence of single phase hexagonal wurtzite lattice structure of ZnO without the signature of any impurity phases. Also, hydrothermally prepared rod like co-doped ZnO nanoparticles consist large number of defect centers at the surface and the presence of such defect centers were confirmed by the Raman and photoluminescence studies. The magnetic measurements of Co and Cu co-doped ZnO nanoparticles using SQUID magnetometer reveal the presence of magnetic ordering and the enhancement of the magnetization of the co-doped ZnO system at room temperature as compare to undoped/mono-doped ZnO nanoparticles. The presence of ferromagnetic ordering together with paramagnetic contribution in the Co and Cu co-doped ZnO sample was confirmed by the fitting of M-T curve using 3D spin wave model and Curie-Weiss law in the temperature range of ∼300 K down to ∼5 K. Our result suggests that the magnetic properties are strongly correlated to the structural defects and grain boundary defects. Also, the large dielectric response of the co-doped ZnO nanoparticles appears due to the trapping of the free charge carriers by the defect centers present at the surface of the rod like Co and Cu co-doped ZnO nanoparticles. These modulations as well as the enhancements of magnetic and dielectric response of the co-doped ZnO nanoparticles are very much useful for many magneto-dielectric device applications.