Ni–Ga and Mg–Ga co-substituted sintered CoFe2O4 ceramics: Studies of their magnetic and magnetostrictive properties

Abstract

Magnetostrictive smart materials (MSMs) with superior magnetostriction parameters (strain (λ) and strain sensitivity (dλ/dH)) are indispensable components for device applications in actuators, torque sensors, and transducers. This study investigates the magnetostrictive characteristics of sintered CoFe2O4 (CFO), Co0.85Ni0.15Fe1.85Ga0.15O4 (CNFGO15) and Co0.85Mg0.15Fe1.85Ga0.15O4 (CMFGO15) ceramics synthesized via a solution combustion method, followed by palletisation and sintering (1350 °C for 2 h). It is revealed from interpretation of XRD data of as-synthesized samples that ferrite powders are single phase and nanosized. This means that post-synthesis calcination is not requisite. According to Rietveld refinement analysis performed on powder data of sintered samples, sintered compositions are single phase, and unit cell parameters are 8.38501, 8.37585 and 8.37664 Å for CFO, CNFGO15 and CMFGO15, respectively. Raman bands, more than five, have been detected in the samples' Raman spectra, due to the mixed spinel structure of the materials. The co-substitution induced substantial grain growth, and the mean grain size follows the order of CMFGO15> CNFGO15>CFO. EDS spectra suggested that compositions stoichiometry is maintained. The chemical state and cation distributions of sintered CFO, CNFGO15 and CMFGO15 samples were studied using their XPS data. Despite high co-substitution in CNFGO15 and CMFGO15 samples, their saturation magnetization (MS) is comparable with the CFO sample value because both tetrahedral (A-site) and octahedral (B-site) sites are diluted equally. However, other magnetic parameters such as coercivity (HC), anisotropy constant (K1), Curie temperature (TC) of CNFGO15 and CMFGO15 are low compared to pristine CFO sample values. The CMFGO15 sample exhibited enhanced λ and dλ/dH at low magnetic fields against the other two samples. Furthermore, the maximum strain sensitivity [dλ/dH]max of CMFGO15 sample is −1.93 × 10−9 m/A at 30 kA/m. This is nearly 160% higher than the values found for other two samples even at remarkable low field.