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Defects and defective technology are considered to be an efficient method for improving electromagnetic wave (EMW) absorption performance. In this study, W-type barium hexaferrite BaCo2Fe16O27 (BCFO) composites with Sm doping were synthesized by a simple ball milling and subsequent annealing process. The phase structure characteristics, magnetic properties, and microwave absorption performance of the BCFO composites were systematically investigated. Specifically, Sm-doped and annealed BCFO composites demonstrated outstanding microwave absorption characteristics because of the efficient interaction between ideal impedance matching and large dielectric loss, specifically, a minimum reflection loss (RL) value of −28.57 dB at 8.5 GHz with 3 mm thickness. Moreover, a broad effective absorption bandwidth reaches 11 GHz, covering the range of 7–18 GHz. It is believed that defects and vacancies induced by Sm doping or annealing in the Ar atmosphere may be an effective means for enhancing microwave absorption, and related mechanisms are discussed in detail. [ABSTRACT FROM AUTHOR]

The NiFe2O4 (NFO) assembly was synthesized via thermal decomposition in a gradient magnetic field, and its structure, composition, as well as magnetic and electromagnetic absorption properties were investigated. The applied magnetic field adjusts the size of nanoparticles, the magnetic properties change correspondingly. The saturation magnetic intensity increases from 54.21 emu/g to 61.67 emu/g, however, the coercivity changes less, and Hc is in the range of 32.75–34.01 Oe. Simultaneously, the XPS results suggest that an increase in oxygen vacancies with addition of magnetic field. With the magnetic field application, a higher complex permittivity and more excellent microwave absorption performance are achieved. With the application of magnetic field, the nanoparticles become smaller, and more interfaces are generated, the interfacial polarisation effect is strengthened. Simultaneously, the applied magnetic field also leads to an increase in oxygen vacancies. Therefore, dielectric loss values are enhanced. Moreover, the reflection loss was optimized to − 14.32 dB with a matching thickness of 5.5 mm when the sample prepared under magnetic field 0.32 T. The above results prove that the magnetic field can be used as an effective route to achieve excellent microwave performance for NFO. [ABSTRACT FROM AUTHOR]