The role of La3+ substitution in modification of the magnetic and dielectric properties of the nanocrystalline Co-Zn ferrites

Abstract

Co-Zn spinel ferrites with lanthanum (La3+) ion substitutions having formula Co0.7Zn0.3LaxFe2-xO4 (x = 0.0, 0.025, 0.05, 0.075, 0.1) were prepared using sol gel auto ignition route. The structural characterization of the ferrites was performed by the x-ray diffraction (XRD) method. The parameters calculated from the XRD analysis include lattice parameter, density, porosity, crystal size and lattice strain. The nanocrystallinity of the ferrite samples was observed with the crystallites of 20–30 nm size. The scanning electron microscopy (SEM) was employed to analyse the morphology of the ferrite crystals. The size and shape of the ferrite nanocrystals were confirmed from transmission electron microscopy (TEM) images. The crystal planes revealed from XRD calculations were confirmed by the selected area electron diffraction (SAED) analysis of the ferrites. Vibrating sample magnetometer (VSM) measurements of the ferrite samples were performed to study the magnetic properties of the ferrites. The effects of the La3+ substitution were observed on the coercivity and saturation magnetization of the ferrites. The variation of dielectric properties of the ferrites within 50 Hz to 5 MHz frequency band were studied at room temperature. The dielectric relaxation in the ferrites was governed by the electron hopping between divalent (Fe2+ and Co2+) and trivalent (Fe3+ and Co3+) cations. Remarkable impact of La3+ composition and the crystal size was observed on dielectric constant as well as loss tangent.