Crystal structure and enhanced magneto-electric properties of cobalt-substituted nickel–zinc ferrite

Abstract

In this work, Ni_0.7−xZn_0.3Co_xFe₂O₄ (x = 0, 0.05, 0.10, 0.15 and 0.20, NZCF) ferrites were successfully fabricated by solid-state reaction method. We have been more focused on the effects of cobalt-substituted NiZn ferrite on crystal structure, microstructure and magneto-electric properties. With gradual addition of cobalt content, since the smaller ionic radius and larger atomic weight of the cobalt, which leads to decrease lattice parameter (a) and enhance X-ray density (d_x), respectively. The grain size (D) increases (4.86 ± 1.10 to 6.26 ± 1.67 μm). When x = 0.05, the initial permeability (μ_i) of NiZnCo ferrites reaches the maximum value. The saturation magnetization (Ms) is firstly decreased slightly from 78.96 to 77.96 emu/g when x ≤ 0.10, then increased to 83.14 emu/g (x = 0.15), ultimately decreased to 81.54 emu/g. Meanwhile, the coercivity (Hc) is dropped from 19.95 to 13.25 Oe when x ≤ 0.05, and stabilized at about 13.40 Oe when x > 0.05. From the dielectric spectrum, the real dielectric constant (ε′) exhibits typical relaxation-dispersion behavior with increasing frequency. The resistivity temperature spectrum also shows good performance: both dc resistivity (ρ) and activation energy (E_ρ) increase with the Co substitution. Here, we have developed a NiZnCo ferrite when Co-substituted x = 0.05 with the highest permeability (μ_i, 123@10 kHz), higher saturation magnetization (Ms, 78.25 emu/g) and lowest coercivity (Hc, 13.25Oe), which is expected to be used in high-frequency capacitors and inductors.