Effects of ordered mesoporous structure and La-doping on the microwave absorbing properties of CoFe 2 O 4

Abstract Low-density ordered mesoporous CoFe 2 O 4 (O CFO) and CoLa 0.12 Fe 1.88 O 4 (O CLFO) are prepared by nanocasting method using mesoporous silica SBA-15 as a hard-template. The crystal structure, surface chemical state, magnetic properties and electromagnetic parameters are characterized by X-ray diffraction, transmission electron microscopy, N 2 adsorption-desorption measurement, X-ray photoelectron spectroscopy, physical property measurement system and vector network analyzer. The results show that all the samples formed a single phase with cubic spinel structure. Meanwhile O CFO and O CLFO possess a highly ordered mesostructure. Comparing with particle CoFe 2 O 4 (P-CFO), O CFO with high specific surface area exhibits lower magnetic saturation ( M s ), higher imaginary part of complex permittivity ( e ′′) and imaginary part of the complex permeability ( μ ′′). The minimum reflection loss ( R L ) of O CFO reaches −27.36 dB with a matching thickness of 3.0 mm. The enhancement of the microwave absorbing performances of O CFO can be mainly attributed to the good impedance matching, high electromagnetic wave attenuation and multiple reflections of electromagnetic wave originated from the ordered mesoporous structure. The M s of O CLFO decreases after La 3+ doping, while the specific surface area, coercivity value, e ′′ and μ ′′ of O CLFO increase. The minimum R L of O CLFO reaches −46.47 dB with a thickness of 3.0 mm, and the effective absorption frequency bandwidth reaches 4.9 GHz.