Fiber-guided and particle-localized microwave absorption of nanoscale CoFe2O4 derived from citric acid-based precursor

CoFe2O4 fibers and particles were prepared by directly annealing electrospun citric acid-based precursor fibers and dried precursor gel under protective atmosphere, respectively. Their electromagnetic parameters were measured and CoFe2O4 nanofibers exhibit excellent microwave absorption performance. When the matching thickness of CoFe2O4 fibers is 3 mm, the bandwidth corresponding to reflection loss below −10 dB (over 90% microwave absorption) can reach 10.0 GHz and cover the entire X-band and Ku-band. Typical Cole-Cole semicircles suggest that both CoFe2O4 particles and fibers have multiple dielectric relaxation processes. The nanoconfinement of the electrospun CoFe2O4 fibers can result in an improved mutual interfacial polarization. For the intrinsic shape anisotropy of the fibrous structure, CoFe2O4 fiber with higher coercivity increases the magnetic loss. Based on comprehensive experimental investigation, the relationship between the microwave energy loss and the morphology of CoFe2O4 is discussed.