Dynamic magnetic characteristics of a composite polymeric material based on carbonyl iron

Abstract

Nowadays microwave radiation is used not only in special means: consumer devices of high-frequency radio electronics move actively ahead, including mobile telephones, computers, and photo- and videocameras. Due to mastering of gigahertz frequencies, miniaturization, small weight, and high speed of modern hardware is provided. Active mastering of the microwave range has aggravated the need for magnetic materials absorbing electromagnetic radiation. Such materials are required to reduce harmful influence on biological objects, to provide electromagnetic compatibility of units and blocks of high-frequency devices, and to construct anechoic chambers. Magnetic elastomers representing composite microwave materials put on metal surfaces whose main components are ferri- and ferromagnetic fillers are used as absorbers [1]. Carbonyl iron is one of the perspective materials for manufacturing absorbing coatings [2]. The frequency band of natural ferromagnetic resonance (NFMR) in the presence of the domain structure lies generally in the limits from 2πf1 = γHa to 2πf2 = γ(Ha + 4πМS) [3]. The anisotropy field of carbonyl iron is Ha ≈ 500 Oe, its saturation magnetization is MS ≈ 1.7⋅10 3 G, and γ/2π = 2.8 GHz/kOe, that is, the NFMR frequency band lies in the limits from f1 ≈ 1.4 GHz to f2 ≈ 61 GHz. Samples of composite materials consisting of P-10 grade carbonyl iron powders in polyethylene matrix were fabricated. Powders of the given iron grade have bulbous structure with average particle sizes of ~3.5 μm. The thickness of the examined plane samples was 1 mm, and the volume iron contents were 50 and 15%. To measure the magnetic permeability (μ = μ′ – iμ″) and the dielectric permittivity (e = e′ – ie″) spectra, a Universal Broadband Radiospectrometer was used based on an E8363В Vector Circuit Analyzer of the Agilent Technologies. Measurements were performed in the frequency range 10 MHz – 20 GHz. A coaxial waveguide, an irregular microstrip resonator [4], and a set of rectangular multimode volume resonators were used as measuring cells [5].