Synthesis, microstructure, dielectric and magnetic properties of Cu substituted Ni–Li ferrites

Cu substituted Ni–Li spinel ferrites were prepared by a conventional sol–gel auto-combustion method. The structure, surface morphology, dielectric and magnetic properties were investigated by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, impedance spectroscopy and vibrating sample magnetometer, respectively. X-ray diffraction studies reveal the single phase spinel structure of the ferrites and the crystallite size varies from 23 to 35 nm. Incorporation of Cu in the Ni–Li ferrites increases the grain size. The dielectric parameters such as ε´, ε′′, loss tan δ and ac conductivity (σac) have been measured for the annealed samples in the temperature range from 35 to 200 °C and over the frequency range from 101 to 107 Hz. The saturation magnetization and coercivity show a dependence on the composition and microstructure. The values of saturation magnetization vary from 25.6 to 33.6 emu/g with increase in x for samples annealed at 600 °C. The values of the coercivity increase from 170 to 203 Oe with increase in x.

Research Highlights
► Cu2+ ion doped Ni0.5Li1.0−2xCuxFe2O4 ferrites have been synthesized by sol-gel auto combustion process.
► With increase in concentration of Cu2+ ions, the lattice constant increases.
► Dielectric constant, tanδ and ac conductivity increase with grain size of the crystal.
► Saturation magnetization first increases with the addition of Cu2+ ions and then decreases.
► Coercivity increases with the increase in the concentration of Cu2+ ions.