Exposed Surface Regulation of MnO ₂ Semiconductor in Cobalt‐Based Magnetic‐Dielectric System Toward Low‐Frequency Electromagnetic Wave Absorption

Abstract Facing increasing absorption requirements for the low‐frequency (2–8 GHz) electromagnetic wave (EMW) energy, dielectric‐magnetic heterojunction design is heading toward a bottleneck. Herein, a unique exposure surface strategy is induced to modulate the dielectric polarization behaviors via the electronic structure manipulation. Multi‐heterointerface Co/MnO/MnO ₂ (CMM) architecture with controllably tuned exposed (131) surface is developed to improve low‐frequency EMW absorption performance. Notably, increased exposure of the (131) surface in MnO ₂ semiconductors significantly enhances polarization effects, which further optimizes impedance matching and boosts attenuation capability, thereby enabling 2–8 GHz frequency‐tunable absorption. The interface engineering‐mediated exposed surface and heterointerface synergistic strategy enables fundamental regulation of dielectric properties and loss mechanisms. The optimized CMM composite demonstrates a strong EMW absorption capability with a minimum reflection loss of −48.3 dB at 3.92 GHz, the effective absorption bandwidth covering 54% of the 4–8 GHz band. Meanwhile, it exhibits exceptional multifunctionality, including excellent thermal conductivity and enhanced mechanical properties. This breakthrough study provides a novel strategy for controlling interface polarization by exposed surface engineering, paving the way for high‐performance, low‐frequency EMW absorbing materials.