Microstructure, lattice strain, magnetic and magnetostriction properties of holmium substituted cobalt ferrites obtained by co-precipitation method

Highlights: • Successful synthesis of Ho doped Co ferrite for low concentrations of Ho ion. • Interesting results obtained in magnetization and magnetostriction data. • Well accounting of and sufficient explanation given for the obtained results. • Stress sensitivity suggests application of these materials in sensing devices. The CoHo_xFe_2-xO₄ (x = 0.00, 0.05, 0.1, 0.15, 0.2) samples were synthesized by chemical co-precipitation technique. The structural properties were studied using X-ray diffraction (XRD). XRD data reveal formation of single cubic spinel phase for the samples having lower concentration of holmium substitution namely x = 0.0, 0.05 and 0.10, However, at higher concentrations, x = 0.15 and 0.2 few extra diffraction lines belonging to HoFeO₃ were observed indicating solubility limit of holmium in the CoFe₂O₄ lattice. Williamson – Hall plot was used to determine strain in the samples. Microstructural studies carried out using Scanning Electron Microscopy (SEM) depict significant changes in microstructure with increase in holmium concentration. Microstructure of un-substituted cobalt ferrite sample was found to be very compact and grain growth was further found to be restricted with increase in holmium concentration. DC magnetization recorded using Vibrating Sample Magnetometer (VSM) at room temperature indicates decrease in saturation magnetization with increase in Holmium concentration, which is correlated with the weakening of A-B exchange interactions. Comparatively high values of coercivity and retentivity are obtained for holmium concentration with x = 0.15. Magnetostriction measurements were carried out for two different orientations of strain gauge fixed on plane surface of sample with parallel and perpendicular orientation with respect to direction of external magnetic field. For un-substituted cobalt ferrite sample, maximum value of magnetostriction was found to be −228 ppm at 3.5 kG magnetic field. This suggests its application in actuator. Further, effect of holmium substitution on magnetic and magnetostrictive properties has been analyzed.