Tunable magnetic and microwave absorption properties of Sm1.5Y0.5Fe17-xSix and their composites

In this work, we report the magnetic and microwave absorption properties of the Sm_1.5Y_0.5Fe_17-xSi_x (0.0 ≤ x ≤ 1.5) and their paraffin composites. It was found that the introduction of Si can remarkably tune the intrinsic magnetic properties of the Sm_1.5Y_0.5Fe_17-xSi_x, making the Sm_1.5Y_0.5Fe_17-xSi_x-paraffin composites excellent microwave absorption materials. The milled Sm_1.5Y_0.5Fe_17-xSi_x powders have flake-like shape with length of 5 μm and thickness of 100 nm, consisting of sphere-like crystalline grains with size of about 11 nm. In the tested frequency region, the permeability μ′ of the composites shows, especially at higher frequency, little decrease after introducing the Si, while the permittivity ε′ decreases by about 40% with Si content increasing from x = 0.0 to x = 1.5, which is advantageous to improve the impedance match and enhance the performance of the microwave absorption. The peak frequency (f_p) of the reflection loss (RL) peak with same composite thickness increases with increasing the Si content, in accordance with the variation of the calculated resonance frequency ^*f_r = f(M_s, H_aθ, H_aφ, μ_i). Moreover, the qualified bandwidth (QB, RL ≤ −10 dB) also increases remarkably with increasing the Si content due to a better impedance match. An extraordinary dielectric microwave absorption peak was also found in the composites, which can further increase the QB in some degree. A maximum RL of −55.1 dB and a QB of 3.7 GHz (12.7–16.4 GHz) are obtained for the Sm_1.5Y_0.5Fe_15.5Si_1.5-paraffine composite, suppressing many reported microwave absorbing materials.