The influence of Nd substitution in Ni-Zn ferrites for the improved microwave absorption properties

Nanocrystalline Ni-Zn ferrites with different neodymium contents (Ni0.5Zn0.5NdxFe2-xO4) were synthesized by sol-gel route combined with self-propagating combustion (SPC) method. The presence of surface functional groups, crystal structure and morphology of the samples were studied by FT-IR, XRD and SEM. The results show that the prepared samples are composed of spinel phase under the condition of low neodymium content, like the pure Ni-Zn ferrite. While neodymium oxide appears after the content of Nd3+ exceeds a certain limit (x > 0.04) and there exist two phases in the ferrite. The results of vibrating sample magnetometer (VSM) and vector network analyzer (VNA) show that adjusting the content of Nd3+ is significant in improving the dielectric properties and microwave absorption capacity of the materials, specifically at low frequencies. When x < 0.04, the enhancement of dielectric loss ability of spinel ferrites by doping Nd3+ is the dominant factor affecting microwave absorption ability of samples. The secondary phase Nd2O3 hardly appears under this condition, thus the weakening effect of Nd3+ addition on magnetic loss ability is not obvious. When x = 0.04, the optimal absorption peak of the material reaches -20.8 dB at 4.4 GHz with a thickness of 8.5 mm and the effective absorption bandwidth (R-L < -10 dB) was 3.2 GHz. On the contrary, when x > 0.04, the magnetic loss ability decreases rapidly (e.g., Ms decreases from 82.47 emu/g to 59.77 emu/g). Meanwhile, the dielectric loss increases slowly and the microwave absorption capacity decreases.