Size-Controllable Synthesis of Fe 3 O 4 Nanospheres for Electromagnetic Wave Absorber

We present a hydrothermal method to control the size of Fe 3 O 4 nanospheres by adjusting the concentration of FeCl 3 ·6H 2 O in ethylene glycol/diethylene glycol binary solvent mixtures. The electromagnetic wave absorption properties of Fe 3 O 4 nanospheres of different diameters have been investigated using a vector network analyzer. The reflection loss of Fe 3 O 4 nanospheres/paraffin wax composite can reach as high as −30.00 dB at 17.50 GHz and −37.95 dB at 7.67 GHz for Fe 3 O 4 nanospheres with diameter of about 120 nm and 170 nm, respectively. The absorption bandwidth with reflection loss below −10 dB is up to 7.01 GHz when the Fe 3 O 4 diameter is about 220 nm. In contrast, the bandwidth decreased to 4.28 GHz when the size shrank to 70 nm. Therefore, our method can be utilized to precisely control the size of Fe 3 O 4 nanospheres in order to manipulate their electromagnetic wave absorption properties.