Dielectric relaxation, conductivity behaviour and magnetic properties of Mg substituted Ni–Li ferrites

The dielectric properties of Mg substituted Ni–Li spinel ferrites synthesized by sol–gel auto combustion process have been studied using impedance measurements in the frequency range from 10 Hz to 10 MHz and in the temperature range from 310 K to 473 K. The effect of frequency, temperature and composition on dielectric constant (ɛ′), dielectric loss (tan δ) and conductivity (σ) has been discussed in terms of hopping of charge carriers between Fe2+ and Fe3+ ions. The electrical modulus formulism has been employed to study the relaxation dynamics of charge carriers and the results indicate the presence of non-Debye type of relaxation in the present ferrites. Similar values of activation energies for dc conduction (Edc) and for conductivity relaxation (EM″) reveal that the mechanisms of electrical conduction and dielectric polarization are same in these ferrites. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of dynamical process for charge carriers. The saturation magnetization and coercivity have been calculated from the hysteresis loop measurements and show striking dependence on the composition.

► The XRD patterns reveal the spinel structure of the annealed ferrites.
► The electrical modulus formulism has been employed to study the relaxation dynamics of charge carriers and the results indicate the presence of non-Debye type of relaxation in the present ferrites.
► A single ‘master curve’ for normalized plots of all the modulus isotherms indicates the temperature independence of dynamical process for charge carriers.
► Saturation magnetization first increases with the increase in the concentration of Mg2+ ions due to increased magnetization of B-site and then decreases because of the antiparallel spin coupling.