Cation distribution by Rietveld technique and magnetocrystalline anisotropy of Zn substituted nanocrystalline cobalt ferrite

Graphical abstract: (a) Saturation magnetization (b) coercivity (c) magnetocrystalline anisotropy constant with the Zn concentration of the samples CoZnxFe2−xO4 (x = 0.0–0.3) annealed at 600 °C. Saturation magnetisation and magnetoocrystalline anisotropic constant increase up to x ⩽ 0.15 and then decrease with the Zn concentration. It is due to the change is distribution of cations in tetrahedral and octahedral sites of spinel ferrites. Highlights: ► Substitution Zn at the Fe site increase magnetocrystalline anisotropy up to x ⩽ 0.15. ► Saturation magnetisation increase up to x ⩽ 0.15. ► For x ⩾ 0.15 saturation magnetization and magnetic anisotropy decrease. ► It is due to change in distribution of cations in tetrahedral and octahedral sites. ► Annealing at 200 °C, superparamagnetic nature has been observed for x = 0.15–0.3. - Abstract: Zn2+ ion substituted nanocrystalline cobalt ferrite materials with the chemical formula CoZnxFe2−xO4 for x = 0.0, 0.1, 0.15, 0.2, 0.25 and 0.3 have been synthesised by standard citrate precursor method. The crystal structure and phase purity have been studied by powder X-ray diffraction (XRD) method by employing Rietveld refinement technique. The cation distribution between the tetrahedral site (A-site) and octahedral site (B-site) has been determined by Rietveld analysis. The distribution of cations changes with the Zn2+ concentration. Average crystallite size and lattice constant increase with the annealing temperature. The lattice constants decrease with the increasing Zn concentration. The vibrational modes of the octahedral and tetrahedral metal complex in the sample have been carried out using Fourier transform infrared spectroscopy (FT-IR). The FT-IR spectra of the sample have been studied in the wave number range of 380–800 cm−1 and it shows the presence of absorption bands which are assigned to tetrahedral and octahedral metal complexes. The elemental analysis has been carried out using energy dispersive spectroscopy (EDS) with the help of Field Emission Scanning Electron Microscope (FE-SEM) and the results reveal that the elements are as per the stoichiometric ratio in all the samples. The Magnetic hysteresis loop measurements were carried out at room temperature using a vibrating sample magnetometer (VSM) over a field range of ±2 T. Annealing at 200 °C, superparamagnetic nature has been observed for compositions x = 0.15–0.3. The magnetic data in saturation have been analysed by employing the law of approach (LA) technique. The saturation magnetisation increases with the Zn for x ⩽ 0.15 and then decreases. The coercivity decreases with the increasing Zn concentration for 600 °C annealed samples. The magnetocrystalline anisotropy constants are found to increase for x ⩽ 0.15 and then decrease with the Zn concentration.