Magnetic field-induced construction of radial ZnO/graphene heterojunctions and defect engineering for enhanced microwave absorption performance.

ZnO/graphene microwave absorbers conventionally rely on static parameter adjustment for morphological control and predominantly operate through dielectric loss, limiting the possibilities for dynamic structural regulation and magnetic-loss contribution. To address this, a magnetic-field-assisted steam-thermal method was developed to simultaneously regulate the morphology and defect-related chemical environment of ZnO/graphene heterostructures. Under a 0.5 T magnetic field, ZnO grows into a radial flower-like nanorod architecture that modifies the effective graphene conductive network and promotes heterogeneous ZnO/graphene interfaces. Meanwhile, magnetic-field-assisted synthesis modifies the defect-related chemical and paramagnetic environments of the composites, which may contribute to polarization relaxation and the observed weak magnetic response. These coupled structural and electromagnetic effects promote interfacial polarization, enhance electromagnetic attenuation, and contribute to favorable impedance matching. The optimized M5 sample achieves a minimum reflection loss of -24.94 dB at a thickness of 1.5 mm, with an effective absorption bandwidth of 1.45 GHz. This work demonstrates that magnetic-field-assisted regulation of morphology and defect-related electromagnetic response provides a promising strategy for designing high-performance ZnO/graphene microwave absorbers.