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

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.