Nd2Fe17N3 powders with planar magnetocrystalline anisotropy for sub-terahertz broadband absorbers

This study investigates the application of the Nd2Fe17N3 compound with planar magnetocrystalline anisotropy as an electromagnetic wave absorber in the gigahertz (GHz) band. We measured the complex permeabilities of two sheets prepared using single-phase Nd2Fe17N3 powders with particle sizes of 3 and 9 μm, which were synthesized through the reduction-diffusion process using the free-space method from 1 to 330 GHz. We discovered a positive imaginary part of complex permeability (μ″) over an extremely wide bandwidth from 1 to 330 GHz and beyond, which was not observed in other materials. To investigate the factors causing μ″ to be positive over this broad high frequency range, we estimated the natural resonance frequency from the saturation magnetization (Ms) and magnetocrystalline anisotropy fields (μ0Ha1 and μ0Ha2) measurement, in combination with magnetic domain pattern observation. We estimated Ms, μ0Ha1, and μ0Ha2 to be 1.73, 0.14, and 17 T, respectively. The natural resonance frequency calculated from these results was 43–166 GHz. Therefore, we speculate that resonance phenomena in Nd2Fe17N3 at frequencies exceeding 166 GHz arise from mechanisms other than natural resonance.