Enhanced magnetostriction of Co–Ni-ferrite composites derived from hard (CoFe2O4) and soft (NiFe2O4) magnetostrictive phases

Abstract

We report on the enhanced magnetostrictive characteristics of composites derived from the hard cobalt ferrite (CoFe2O4; CFO) and soft nickel ferrite (NiFe2O4; NFO) materials. The CFO, NFO and CFO-NFO (CNFO) mixed composites (25NFO + 75CFO, 50NFO + 50CFO and 75NFO + 25 CFO) were synthesized by employing a cost-effective and eco-friendly glycine-nitrate autocombustion method. The CFO, NFO and their mixed composites were evaluated to assess their phase purity, surface morphology, magnetic properties, and magnetostrictive characteristics. The X-ray diffraction (XRD) and electron microscopy analyses revealed that the CFO and NFO nanomaterials were phase pure, porous in nature, and nano-sized with average crystallite size of 73 nm (CFO) and 69 nm (NFO). Subsequently, the Co–Ni-ferrite composite made from CFO and NFO in equal quantity by sintering at 1200 °C indicate that the lattice parameter, a, of the composite lies in between the lattice parameters of respective components (CFO-8.390 Å and NFO-8.343 Å) indicating that both phases co-exists as single-phase in the composite. The grains of the sintered compounds are nearly spherical shape with the average sizes ∼670 nm, ∼550 nm and ∼560 nm, respectively, for CFO, NFO and 50NFO +50CFO composite. Due to grain growth upon sintering, magnetizations of the sintered CFO and NFO nanomaterials are higher than that of as-synthesized samples. Interestingly, the magnetization curves of sintered CNFO composites exhibit symmetric nature (single loop), where their magnetization lies in between the magnetizations of NFO and CFO phases, indicating a proper exchange coupled between the two phases. The composites demonstrate better magnetostriction at lower magnetic fields than the parent sintered CFO and NFO samples. At an applied magnetic field of 2 kOe, the obtained magnetostriction value for 50NFO +50CFO composite (−120 ppm) is nearly 500% higher than that of CFO (−20 ppm) and 300% higher than that of NFO (−30 ppm). The structure-phase-property correlation established in these composites expected to provide a road-map for their possible applications in electromagnetic devices.