Atomic‐Scale Regulation of Spin Polarization in High‐Entropy Frameworks for Efficient Low‐Frequency Electromagnetic Wave Attenuation

High‐performance electromagnetic wave (EMW) absorption in the low‐frequency S and C bands (2–8 GHz) remains challenging due to fundamental constraints like the Snoek limit and difficulty in achieving proper impedance matching, which conventional ferromagnetic materials cannot overcome through extrinsic morphology engineering alone. Here, an electronic‐structure‐driven strategy is reported to design a series of (Fe, Co, Ni, Cu, and Cr)Se 2 high‐entropy selenides (HESe) that translate atomic‐scale orbital regulation into enhanced macroscopic EMW absorption. By integrating magnetic elements (Fe, Co, and Ni) with trivalent chromium, the distinctive t 2g 3 e g 0 electron configuration of the Cr (III) ion generates high spin polarization and strengthened spin‐orbit coupling, which increases the magnetocrystalline anisotropy constant (K) and shifts magnetic resonance toward the low‐frequency region without compromising saturation magnetization. Moreover, controlled introduction of Se vacancies further modulates the dielectric environment by inducing lattice distortion and interfacial polarization, thereby optimizing impedance matching. As a result, the vacancy‐engineered pentanary material (HESe‐V r ) exhibits a minimum reflection loss of −50.13 dB at 2.92 GHz with an effective bandwidth spanning the S and C bands. This work demonstrates that d‐orbital electron configuration engineering in high‐entropy compounds provides a viable route for tailoring intrinsic electromagnetic responses, offering a new paradigm for the rational design of next‐generation EMW absorbing materials.