Magnetic Composite Formed by Exsolution for Enhanced Exchange Coupling and Breaking the Permeability‐Frequency Limitation

Abstract

ABSTRACT The development of ferrite‐based absorbers for high‐frequency integrated electronics and fifth‐generation (5G) communication systems has long been constrained by the Snoek limit, which causes a pronounced deterioration of complex permeability in the gigahertz (GHz) range. Here, we overcome this bottleneck by constructing well‐dispersed and rigidly anchored CoFe phases within a W‐type hexaferrite matrix through an in situ thermal‐exsolution strategy, yielding coherent alloy/oxide heterostructures. The nanoscale interfaces establish strong exchange coupling and tailored local anisotropy, which stabilize the real permeability and extend natural resonance for magnetic loss across 2∼8 GHz, effectively surpassing the Snoek limit. The resulting composite achieves an absorption bandwidth of 7.7 GHz at 1.4 mm, enabled by balanced impedance matching and enhanced attenuation capability, and offers a practical route for mitigating 5G electromagnetic interference. This study provides a link between macroscopic permeability parameters and nanoscale magnetic configurations, guiding the design of high‑performance magnetic‐response materials.