Preparation and microwave absorption properties of Ni–Co nanoferrites

• NixCo1−xFe2O4 were directly obtained by microwave assisted ball milling at 2.45 GHz.
• All the synthesized ferrite had more excellent magnetic properties.
• The lowest reflection factor is observed for (x = 0.8) at 11.52 GHz is −36.2 dB.
• The absorbing bandwidth with RL below −10 dB is in the range of 9–12 GHz.

NixCo1−xFe2O4 (x = 0.2, 0.5, 0.8) particles were prepared by a self-designed method, i.e., microwave assisted ball milling. A series of characterizations were carried out on the prepared powders, including X-ray Diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). XRD and TEM results indicated that the particles are well-crystallized and the average size is about 15 nm. According to VSM results, the Ms values are 76 emu/gm, 61 emu/gm and 46 emu/gm respectively, which obviously presented higher saturation magnetization values compared with other existing methods. Complex permittivity and permeability of Ni–Co ferrites were explored by VNA in the frequency of 2–18 GHz, and the reflection loss (RL) was also calculated. The results illustrated that the minimum reflection loss values of the three ferrites all emerged in the range of 9–12 GHz, and the Ni0.8Co0.2Fe2O4 with a thickness of 2.5 mm could achieve −36.2 dB at 11.52 GHz, which indicated that the Ni–Co ferrite nanoparticles possessed great potential in microwave absorption applications.