Aluminum and Zinc Co-substituted Cobalt Ferrite: Structural, Magnetic, and Magnetostrictive Properties

Abstract

We report on the influence of Al and Zn co-substitution on the structural, magnetic, and magnetostrictive properties of cobalt ferrite (Co1–xZnxFe2–xAlxO4, 0 ≤ x ≤ 0.15; CZFAO) materials, which were made using a glycine-nitrate autocombustion process. The cubic spinel structure is present in both the as-synthesized and the sintered CZFAO samples, where it was evident that the crystallite size and lattice parameter reduced with increasing x due to the incorporation of smaller Al3+ ions in place of larger Fe3+ ions in spinel ferrite. Co-substitution induced changes in the metal–oxygen bond lengths, causing both the tetrahedral and octahedral infrared and Raman spectroscopic bands to shift toward higher wavenumbers. The electron microscopy analyses indicate that the Al–Zn substitution induces grain growth, leading to a dense, interconnected grain morphology. Mossbauer analyses indicate that the Al3+ occupies the octahedral site, whereas Zn2+ is substituted at the tetrahedral site. Due to equal magnetic dilution of both tetrahedral and octahedral sites caused by the presence of Zn and Al at the appropriate sites, the saturation magnetization MS of CZFAO is the same as that of pure CFO. All other magnetic parameters (coercivity HC, magnetocrystalline anisotropy constant K1, and Curie temperature TC) decrease with increasing x, where the decline observed is mostly due to superexchange interaction (A-O-B) reduction caused by the substituents’ non-magnetic character. CZFAO materials exhibit higher magnetostriction strain λ and strain sensitivity dλ/dH at relatively low magnetic fields; among all the samples, x = 0.15 demonstrates a maximum strain sensitivity of −2.53 × 10–9 m/A at 23 kA/m magnetic field. The composition-tuned CZFAO materials with desirable properties are suitable for application in torque sensors.