Effects of ordered mesoporous structure and La-doping on the microwave absorbing properties of CoFe2O4

Low-density ordered mesoporous CoFe2O4 (O-CFO) and CoLa0.12Fe1.88O4 (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 CoFe2O4 (P-CFO), O-CFO with high specific surface area exhibits lower magnetic saturation (M-s), higher imaginary part of complex permittivity (epsilon '') and imaginary part of the complex permeability (mu ''). The minimum reflection loss (RL) 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 La3+ doping, while the specific surface area, coercivity value, epsilon '' and mu '' 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. (C) 2017 Published by Elsevier B.V.