Excellent microwave absorption of porous rod spinel by exceeding the Snoek limit via fibrosis and grain refinements

Abstract

Pure spinel ferrite cannot exhibit satisfactory electromagnetic wave (EMW) absorption performance. In this study, single-phase, Co, Ni, and Zn co-doped, porous, defective, nano–microcrystalline self-assembled 1D rod-shaped spinel ferrites were successfully synthesized via a coprecipitation combined thermal decomposition method. The sample Co_0.5Ni_0.2Zn_0.3Fe₂O₄ (C5N2Z3-C) exhibited excellent EMW absorption performance with an RL_min. of −65.4 dB at a thickness of 3.2 mm and an EAB_max. of 7.8 GHz at 2.8 mm. Its excellent EMW absorption performance was confirmed to be due to its specific microstructure, which precisely regulates dielectric loss, breaks the Snoek limit and greatly improves magnetic loss. The EMW dissipation mechanism of the C5N2Z3-C sample was also surveyed in detail, including optimized impedance matching, multiple reflection and scattering, interfacial and dipole polarization, and multiple natural and exchange resonances. Its magnetic properties were controlled through ion doping; magnetic anisotropy field was regulated through the preparation of porous particles with special morphology and polarization loss was improved via abundant fine-grained boundaries, heterogeneous interfaces and lattice defects. Thus, the enhancement of its EMW absorption performance was achieved through multiple regulations.