The microwave absorption performance of NiFe₂O₄ prepared under the gradient magnetic field

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 H_c 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.