# Enhanced electromagnetic wave absorption performance by introducing exchange bias in a CIP@γ-FeOOH heterostructure

## TL;DR

A new method improves electromagnetic wave absorption by creating a core-shell structure with enhanced magnetic properties.

## Contribution

A transition-layer-guided oxidation strategy introduces exchange bias in a CIP@γ-FeOOH heterostructure for better EMW absorption.

## Key findings

- The CIP@γ-FeOOH composite achieves an effective absorption bandwidth of 6.13 GHz.
- The material exhibits a minimum reflection loss of −17.68 dB at 60 wt%.
- The design overcomes the Snoek’s limit constraint through interfacial engineering.

## Abstract

High-performance electromagnetic wave (EMW) absorbing materials are urgently needed to mitigate electromagnetic (EM) pollution. Carbonyl iron powder (CIP), a conventional magnetic loss absorber, often shows limited absorption bandwidth at low filler loadings. Here, we report a transition-layer-guided oxidation strategy to construct a hierarchical CIP@γ-FeOOH core-shell absorber. A sacrificial SiO2 shell enables the uniform growth of a flower-like γ-FeOOH shell while protecting the CIP core. The resultant ferromagnetic/antiferromagnetic (FM/AFM) interface induces a significant exchange bias effect, enhancing magnetic loss via interfacial pinning and strengthening the low-frequency magnetic response. Combined with defect-induced polarization and structural scattering, the composite breaks the Snoek’s limit constraint with a maximum effective absorption bandwidth (EABmax) of 6.13 GHz (9.38–15.51 GHz) and a minimum reflection loss (RLmin) of −17.68 dB at 60 wt. %. These findings provide a structural and mechanistic basis for designing CIP-based EMW absorbers with improved broadband performance through interfacial engineering.

•Sacrificial SiO2 layer regulates oxidation to form CIP@γ-FeOOH•FM/AFM interface induces exchange bias to boost low-frequency magnetic loss•CIP@γ-FeOOH breaks Snoek’s limit with broadband EMW absorption

Sacrificial SiO2 layer regulates oxidation to form CIP@γ-FeOOH

FM/AFM interface induces exchange bias to boost low-frequency magnetic loss

CIP@γ-FeOOH breaks Snoek’s limit with broadband EMW absorption

Physics; Engineering; Materials science