Obtaining Low-Frequency and Broadband Absorbing Ferrite@C Microspheres through the High Entropy Engineering and Construction of Opened-Hollow Multi-Shell Architecture

The flexible manipulation of the position and type of metal cations in spinel ferrites gives the possibility of tuning its dielectric and magnetic properties, thus opening up broad design space for broadband and low-frequency absorption. However, there are still challenges in how to ensure that metal cations of diverse designs can be effectively introduced into the ferrite lattice to form homogeneous entropy-stable compounds, and further engender stable ferrite compounds with special multi-interface and hollow micro-nano structures to achieve lightweight and efficient performance. In this paper, the opened-hollow multi-shell high-entropy (FeCoNiZnMg)Fe 2 O 4 @C microspheres with a controllable carbon-coated triple-shell and entropy-stable ferrite composition are constructed. The designed hollow triple-shell structure enhances the magnetic interactions between the shells and regulates the magnetic domain structures and effective fields. The (FeCoNiZnMg)Fe 2 O 4 @C microspheres achieve an incredibly high absorption strengths (−60.5 dB) and wide effective absorption (9.3 GHz). Meanwhile, the high entropy effect effectively adjusts the anisotropic magnetic field size, significantly improving the low-frequency absorption of 4–8 GH band, far exceeding the performance of ferrite@C materials without forming a high-entropy phase. This unique hollow multi-shell ferrite@C composite based on high entropy strategy offers exciting prospects for rational composition and accurate structure construction for multi-interface polarization and lightweight design.