Sonar—sharper senses in the depths: Tucker, D.G., New Scientist, Vol 41, No 637 (1969) pp 392–394 (1375)

Abstract

Polycrystalline soft magnetic nickel–zinc ferrites with chemical composition Ni1−xZnxFe2O4, where x=0, 0.2, 0.4, 0.6, 0.65, 0.7, 0.75, and 0.8, were prepared by solid state reaction method. We researched the effect of zinc concentration on the lattice parameter, crystal morphology and electromagnetic properties at high frequency. Results show that ε′ and ε″ decline with increasing frequency until they reach almost constants over 3 MHz to 1 GHz. The dielectric constant achieves a maximum when the Zn concentration is 0.8. The value of ε′ slightly declines with increasing frequency in the range of 2–18 GHz. The spectra of the permeability displays a relaxation resonance for the ferrites with x=0, 0.2, and 0.4 in 3 MHz to 1 GHz frequency range. The permeability is ruled by Snoek's law, which results in the values of μ′ decreased fast below 2 GHz and smaller than 1 above 2 GHz. The value of μ′ reaches maximum and μ″ shows minimum for the samples around x=0.75 in 2–18 GHz range. The magnetic permeability μ′ decreases in an external magnetic field, and shows two resonance peaks corresponding to domain wall and spin rotation resonance. The resonance peaks shift to higher frequency with increasing the external magnetic field. But the permeability has no clear response for magnetic field when zinc concentration is much higher.