Microwave absorbers are increasingly being used to enhance shielding performance at higher frequencies. Great effort has been made to develop materials with superior reflection loss (RL), thin thickness, wide bandwidth, and low density to improve their efficiency in electromagnetic microwave absorption. However, for the magnetic absorbing materials, the higher complex permittivity makes the impedance matching effect poorer, and it is hard to obtain a better microwave absorption. In this work, the rare-earth intermetallics La2Fe4Co10B fine powders with planar magnetocrystalline anisotropy and high magnetization were prepared using the hydrogenation desorption (HD) technique. By annealing the obtained magnetic powders at different temperatures in the air to slowly form an oxide layer on their surfaces, its complex permittivity can be significantly reduced without changing its complex permeability, and its microwave absorption can be dramatically enhanced. For the La2Fe4Co10B/paraffin composite, the real part of the complex permittivity at 10 GHz can be reduced from 18.0 to 8.4, with a decreasing range of 53.3%. The reflection loss (RL) is -25.4 dB at 1.6 mm with an effective absorption bandwidth of 6.2 GHz. As an efficient and lightweight absorber, La2Fe4Co10B/paraffin composite has potential application value in constructing new microwave absorber.
Fig.1. Frequency dependence of electromagnetic parameters of La2Fe4Co10B/paraffin composites with different annealing temperatures: (a) the complex permittivity; (c) the complex permeability.
Fig.2. The RL curves with the broadest effective absorption bandwidth of La2Fe4Co10B/paraffin composites with different annealing temperatures.