The Effect of Grain Size on Microwave Electromagnetic Properties of Mn4N

Micro-sized Mn4N powders have been prepared from pure electrolytic manganese powder and ammonia via a convenient route in a tube furnace at 900 ∘C. The synthesized powder was ground with different time, and then sieved under 70, 100, 140, 270, and 400 meshes. The microstructure, morphology, magnetism, and electromagnetic properties were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and vector network analyzer (VNA). The results show that the as-prepared Mn4N is in irregular lump-like shape with different sizes. With the decrease of grain size, the saturation magnetic intensity of Mn4N displays a tortuous increase tendency, and the real parts of complex permittivity show an obvious decrease trends. The real and imaginary permittivity curves display great fluctuation versus frequency at 11–13 GHz. With the decrease of grain size, the real (μ′) and imaginary (μ″) parts of relative complex permeability give an increase and decrease trends, respectively. Mn4N sample with 70 mesh has the optimal absorbing property. The effective absorption bandwidth (reflection loss < −10 dB) can reach 13–15 GHz, which can be attributed to the stronger spontaneous polarization and better magnetic loss for larger Mn4N particles.