Study On Properties Of High Frequency Nickel Zinc Ferrite Matrix Composites

Polycrystalline soft magnetic nickel-zinc ferrites with chemical composition Ni_1-xZn_xFe₂O₄, where x=0,0.2,0.4,0.6,0.65,0.7,0.75,0.8,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 ?'and ?" decline with increasing frequency until they reach almost constants over 3 MHz-1 GHz. The dielectric constant achieves a maximum when the Zn concentration is 0.8.The value of ?' 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= 0,0.2,0.4 in 3 MHz-1 GHz frequency range. The permeability is ruled by the Snoek's law, which results in the values of ?'decreases fastly below 2 GHz and smaller than 1 above 2 GHz. The value of ?'reaches a maximum and ?" shows a minimum for the samples around x= 0.75 in 2-18 GHz range. The magnetic permeability ?'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.The composite ceramics of spinel ferrite Ni_0.4Zn_0.6Fe₂O₄ with high saturation magnetization and tetragonal perovskite Ba_0.6Sr_0.4TiO₃ with microwave dielectric property were synthesized by solid state reaction method. We obtained high dense and pure composite ceramics. The ?'of the composite decreases with frequency increasing from 3 MHz to 1 GHz, and decreases with NZFO content increasing. The ?" of the composite increases with frequency increasing at high frequency range in 3 M-1 GHz. The spectra of the permeability displays a relaxation resonance for the composite in 3 M-1 GHz frequency range. The initial permeability increases with the increasing of NZFO concentration, and the cut-off frequency decreases with NZFO increasing. This phenomenon obeys the Snoek's law ?ifr=constant. The values of ?'of the composite decrease monotonically with the increment of NZFO concentration at 1-5 GHz.The composites with x= 0.6,0.7,0.8,0.9 have a relative higher ?'than the pure NZFO at 1-10 GHz, which is explained by the free electron theory. At the measuring frequency range of 1-10 GHz, the value of ?' shows maximum and ?" shows minimum for the composite with x= 0.6 in all ceramics. The initial permeability of the sintered composite decreases with increasing dc magnetic field at 1?10 GHz. The spectra of permeability shows a domain wall resonance, and the resonance frequency shifts higher with larger dc magnetic field. But the permeability shows relative weak response to the dc magnetic field for the composites with high NZFO concentration.