Remarkable Magnetic Exchange Coupling via Constructing Bi‐Magnetic Interface for Broadband Lower‐Frequency Microwave Absorption

TLDR

Severe lower‑frequency microwave pollution from 5G demands advanced absorbers, yet intense wave‑impedance coupling and limited dissipation hinder performance in the 2–8 GHz range. The study aims to design a hard/soft ferrite heterostructure that overcomes these limitations. Core–shell hard/soft BaFe(12‑x)Co_xO_19@Fe₃O₄ particles were fabricated via spray‑drying and solvothermal synthesis, creating abundant heterointerfaces between hard magnetic cores and soft magnetic shells. The resulting composites exhibit strong magnetic exchange coupling that surpasses Snoek’s limit, achieving a minimum reflection loss of –48.9 dB at 3.5 mm and a –10 dB bandwidth covering 2.6–8 GHz, demonstrating superior lower‑frequency microwave absorption.

Abstract

Abstract Severe lower‐frequency (2–8 GHz) microwave pollution caused by the rapid development of 5th generation (5G) communication posts significance on cutting‐edge microwave absorbers. However, the intensely coupled wave‐impedance and microwave dissipating ability dramatically hinder their performance in the exact lower‐frequency range. The rationally designed heterostructure of hard/soft ferrite composite provides an efficient solution to address the issue. In this context, core‐shell structured hard/soft BaFe (12‐x) Co x O 19 @Fe 3 O 4 with abundant heterointerface is created using facile spray‐drying and subsequent solvothermal approach, where hard magnetic BaFe (12‐x) Co x O 19 serves as the core and soft magnetic Fe 3 O 4 serves as the shell, respectively. The unique core‐shell integration contributes sufficient magnetic exchange coupling interaction for strong magnetic loss beyond Snoek's limitation, which considerably boosts a lower‐frequency microwave absorption. Accordingly, the minimum reflection loss (RL min ) of typical BaFe 11.6 Co 0.4 O 19 @Fe 3 O 4 microcomposite reaches − 48.9 dB at the thickness of 3.5 mm, its bandwidth of reflection loss < − 10 dB can cover almost all the S and C bands (2.6–8 GHz). Generally, an easy and controllable pathway is conveyed in this work to encourage improved magnetic loss ability as well as decouple the wave‐impedance and microwave dissipating ability in magnetic composites, which widens the road to the development of advanced lower‐frequency magnetic absorbers.