Influence of crystal size on structural, magnetic, mechanical, and dielectric properties of Ni-Cu-Zn nanoferrites

The nanocrystalline spinel ferrite, Ni0.3Cu0.2Zn0.5Fe2O4, was prepared by sol–gel self-ignition route. The synthesized samples were annealed at two different temperatures 400 °C and 600 °C for 4 h. The characterization study of these two ferrite samples along with the as-prepared (without annealing) sample was performed by means of X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer, elastic, and dielectric spectroscopy. The formation of the ferrites having single-phase cubic structure was revealed from the analysis of X-ray diffraction patterns. The increase in crystal size with increasing temperature of annealing was obtained from X-ray diffraction data. The lattice constant was increased with the increase in annealing temperature. Transmission electron microscope images exhibit spherical crystalline particles having size in the range of 8 to 12 nm. Analysis of the hysteresis loops obtained by vibrating sample magnetometer shows that as annealing temperature increases, saturation magnetization and coercivity are also increased. Room temperature values of shearing velocity (VS) and longitudinal velocity (VL) are obtained from the Ultrasonic Pulse transmission method, and are employed to determine the elastic moduli and Poisson’s ratio. The values of these moduli are increased with increasing temperature of annealing, which predict the strength of bonding force between atoms. The dielectric parameters viz. dielectric constant (ε') along with corresponding loss (ε") are explained on the basis of hopping mechanism.