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

In this work, Ni 0.7− x Zn 0.3 Co x Fe 2 O 4 ( 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 ( M s) 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 ( H c) 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 ( M s, 78.25 emu/g) and lowest coercivity ( H c, 13.25Oe), which is expected to be used in high-frequency capacitors and inductors.