Microwave Absorption Properties and Characterization of Porous Permanent/Soft Magnetic Composite Iron Nitride with Heterogeneous Interfaces

Abstract

Iron nitride-based composites with different morphologies and magnetic properties are obtained by controlling the nitriding process, thus constructing heterogeneous interfaces conducive to microwave absorption. During the low-temperature nitridation process for synthesizing the permanent magnetic Fe₁₆N₂ phase, a stable soft magnetic Fe₄N phase tends to form on the surface of particles. Consequently, the porous structured Fe₁₆N₂/Fe₄N composites composed of nano-units are prepared by spray pyrolysis and nitriding processes. The microwave-absorbing mechanisms of permanent/soft magnetic composite iron nitride with porous structure has been elucidated by analyzing the microstructure and electromagnetic properties of samples with varying contents of permanent and soft magnetic materials. The composite of permanent and soft magnetic materials not only creates a heterogeneous interface but also generates a magnetic exchange coupling effect, which improves the impedance matching and increases the interface polarization and dipolar polarization. Eventually, through the coordinated action of excellent dielectric and magnetic loss, good microwave absorption properties are achieved: the minimum reflection loss (RL_min) is −48.27 dB and the widest effective absorption bandwidth (EAB_max) is 4.08 GHz with the matching thickness of 1.3 mm. This study provides new insight for further exploration of the application of nano-magnetic materials in the field of microwave absorption.