Mechanistic Insight into the Critical Concentration of Barium Hexaferrite and the Conductive Polymeric Phase with Respect to Synergistically Electromagnetic Interference (EMI) Shielding

We demonstrate the necessity of synergetic absorption and reflection in hard magnetic nanomaterial with conducting polymer for microwave absorption. We investigated various nanocomposites with varied concentrations of phase pure barium hexaferrite (BFO) and polyaniline (PANI) in wax matrix. We found a critical concentration of BFO (Wax: PANI: BFO::50:42:08 wt%, i.e., BFO composition below its percolation threshold) where the Ohmic, dielectric and magnetic losses for the nanocomposites were maximum giving a peak microwave attenuation of 99.85%, out of which 85% attenuation was due to absorption. Beyond this concentration, on either side, the shielding effectiveness decreased. An extraordinary synergy between absorption and reflection was observed when the thickness of the specimen was increased from 1 mm to just 3 mm. The underlying mechanism of synergy was explained via a structural model based on the complex permittivity and permeability values. Our model suggests the necessity of a critical concentration of magnetic materials in a conducting phase for enhancing the microwave absorption.