Attenuating electromagnetic waves
with an absorption-dominant mechanism
is still an arduous challenge, despite the recent progress in fabricating
advanced electromagnetic interference (EMI) shields. In this study,
EMI shielding materials with an outstanding absorption performance
were developed. As such, in the first step, we report a practical
method for synthesizing magnetic Zn0.5Ni0.5Fe2O4 (ZnNiFe) nanoparticles. The magnetic hysteresis
loop reveals that the synthesized magnetic nanoparticles are superparamagnetic
with a saturation magnetization of 75.8 emu/g. Thereafter, we propose
an EMI absorber using a multilayer assembly of polyvinylidene fluoride
sheets containing low concentrations of reduced graphene oxide (rGO)
and ZnNiFe. It is shown that the EMI shielding effectiveness increases
from 23.93 to 29.05 dB, and the shielding by reflection decreases
from 6.5 to 0.5 dB. This happens as the number of layers increases
from two to nine at a fixed total thickness of 1.8 mm and filler loadings
of 1 wt % rGO and 5 wt % ZnNiFe. More importantly, the nine-layer
sample shows an absorption coefficient of A = 0.91,
which translated into absorption of more than 91% of the incident
wave. To the best of our knowledge, this is the highest ever reported
absorbance for a polymer-based EMI shield. It is hypothesized that
the superior absorbance of the nine-layer structure originates from
(1) multiple internal reflections inside the shield due to the presence
of numerous conductive layers and (2) supermagnetic properties of
ZnNiFe nanoparticles, leading to enhanced magnetic loss.