The influence of morphology, structure, and weight fraction of magnetic additives on the electromagnetic characteristics of composites

Abstract

Abstract This study deals with different magnetic additives based on ferrites (MnZn, LaCa (Co and Ti)), carbonyl iron (CI), and iron filaments (IF) formulated in epoxy resin. Morphological and structural characteristics of the additives were evaluated. Based on these additives samples with both different thickness and weight fractions (1–70\u202fwt%) were prepared. The formulated composites were analyzed considering different electromagnetic characteristics: reflectivity, shielding effectiveness, the complex parameters of dielectric permittivity (e) and magnetic permeability (µ), and the corresponding loss tangents in the microwave X-band. Scanning electron microscopy assisted with energy-dispersive spectrometry (SEM-EDS) analyses show that the additives have different morphologies, with varied sizes, shapes, and compositions. X-ray diffraction (XRD) analyses allowed determining the structural phases of the magnetic additives: CI and IF are constituted by Fe-α phase, the ferrite of MnZn has an unique phase, and the two ferrites of LaCa-Co and LaCa-Ti have the same phase in the presence of different metallic oxides. In general, the complex parameters of e and µ increased with the additive concentration increase in the composites, as expected, considering the magnetic characteristics of all additives studied. Reflectivity measurements show different attenuation values with promising results for composites based on CI, IF, and MnZn ferrite. The composites based on the ferrites show the worst performance on the reflectivity measurements. The shielding effectiveness measurements show good results (20\u202fdB) over the entire X-band for specimens based on the LaCa-Co ferrite. In this case, the dominant shielding mechanism is due to the multiple scattering (SEM) in the material.