Electromagnetic wave absorbing properties of Ni-Zn ferrite powder-epoxy composites in GHz range

Spinel ferrites NixZn1-xFe2O4 (x = 0.4, 0.5, 0.6) with grain sizes ranging from tens of nanometers to several hundred nanometers were prepared using the sol-gel and post-annealing processes. X-ray diffraction (XRD) analysis confirmed that a crystalline single spinel phase could be formed after annealing the sol-gel processed powders at >= 400 degrees C. Reflection loss (RL) maps as functions of frequency (100 MHz <= f <= 15 GHz) and sample thickness were plotted for the Ni-Zn ferrite-epoxy (10 wt%) composites. The RL patterns were systematically modulated by the Ni-Zn ferrite grain size and Ni composition x. The electromagnetic wave absorbing area of RL < -10 dB enlarged toward the upper left side of the map as the grain size increased, and it also gradually stretched in the upper-left direction as x changed from 0.4 to 0.6. The x = 0.6 sample showed the largest negative RL peak under - 60 dB at f = 2.9 GHz with a thickness of 5.6 mm. It also exhibited a very broad-ranged electromagnetic wave absorbing performance with a thickness of 3.1 mm, indicated by RL < -10 dB being satisfied in the frequency range of 4-13 GHz.