Oxygen vacancies induced room temperature ferromagnetism and enhanced dielectric properties in Co and Mn co-doped ZnO nanoparticles

Abstract

We investigated the influence of oxygen vacancies (varying) on the structure and properties (dielectric and magnetic) of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles (NPs) fabricated using the chemical precipitation technique. The oxygen vacancies in the lattice increased with an increase in dopants (Co, Mn) concentration. Annealing of the doped nanoparticles decreased their dielectric properties due to reduced grain boundaries caused by enhanced grain growth. Replacement of Zn ions with dopants in the lattice enhanced the samples' electrical conductivities due to the reduction in grain boundaries and increase of charge carriers. The co-doped nanoparticles annealed at 600 °C exhibited some hysteresis loop changes and became ferromagnetic (FM). The magnetization increased with an increase in dopants content in the ZnO matrix, while coercivity decreased. This shows that the properties of the doped samples are strongly related to the number of oxygen vacancies. These results demonstrated that the enhanced dielectric and magnetization responses of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles are strongly correlated with the oxygen vacancies. The enhancement in optical, dielectric, and magnetic properties make transition metals (TM)-doped ZnO nanoparticles suitable for spintronics, and optoelectronic-based applications.