| Summary: | Nickel ferrite powders were prepared by combustion synthesis of Fe, Fe2O3 and NiO using NaClO4 as fuel. Nickel ferrite ceramics were fabricated by single-step and two-step sintering under various conditions. The effects of each sintering process on the densification, microstructure and properties of the ceramics were investigated. X-ray diffraction analysis of as-prepared powders and as-fabricated ceramics confirmed a single-phase NiFe2O4 with a cubic spinel crystal structure. Single-step sintering produced ceramics with a wider density range (3.63–3.97 g/cm3) than two-step sintering (3.74–3.84 g/cm3) and a wider grain size range (1.10–2.31 µm compared to 1.30–1.37 µm). Two-step sintering produced ceramics with greater microhardness (135.00-172.60 HV) than single-step sintering (65.33-153.00 HV). In both methods, higher sintering temperatures produced ceramics with greater saturation magnetization (Ms). The highest Ms values were 62.84 emu/g from single-step sintering at 1200°C and 70.00 emu/g from two-step sintering at T2 = 1150°C: Hc was, respectively, 31.18 and 22.00 Oe. The ceramic sintered by the two-step method at T2 of 1150°C presented superparamagnetic-like behavior of multi-domain magnetic materials, with high µi and very low Hc. The higher electrical resistivity (R), dielectric constant (εr) and quality factor of this ceramic support high-frequency data storage applications.
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