Nickel ferrite ceramics: combustion synthesis, sintering, characterization, and magnetic and electrical properties

Abstract

ABSTRACT 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.