Evolution of electron localization with Co2+ variations in CoxFe3−xO4 hollow spheres for enhanced wave absorption

Substitution can cause changes in electromagnetic parameters thereby affecting the electromagnetic wave (EMW) absorption performance of the material. We inferred that the fundamental reason for the performance improvement is the transitions in the absorption mechanism, which is caused by the change in electronic structure that originated from the substitution. To confirm this, we prepared Co x Fe 3 − x O 4 (0 ≤ x  ≤ 1) hollow microspheres and investigated its absorption performance in 2–18 GHz. Subsequently, a series of theoretical studies were carried out that focusing on the impact of increasing Co 2+ substitution on the electrical and magnetic loss mechanisms, as well as the inherent relationship between the substitution and the absorption performance. The result indicates that in terms of dielectric loss, an increase in Co 2+ substitution can induce a transition from conductivity loss to polarization loss by increasing the number of holes and strengthening the electron localization. Meanwhile, substitution results in a transformation from the eddy current loss to a magnetic resonance mode, and leads to an increase in magnetocrystalline anisotropy simultaneously, enhancing the magnetic loss ability. As a result, the transformation of electrical and magnetic loss mechanisms ultimately leads to an overall improvement in EMW absorption performance of Co x Fe 3 − x O 4 , and CoFe 2 O 4 hollow microsphere consequently realizes an extremely high attenuation performance of −72.3 dB at 2.67 mm. This work provides a deeper understanding of the intrinsic relationship between the macroscopic absorption performance of ferrite and its microscopic electronic structure, which can guide the synthesis of efficient ferrite absorbers.