Tunable magnetocrystalline anisotropy and high-frequency magnetic properties of Y2(Co1−xFex)17 and their composites

Rare-earth transition-metal (R-T) intermetallic compounds are emerging as competitive candidates for novel microwave absorption materials (MAMs) since they show high magnetization and tunable easy magnetization directions (EMDs). In this work, Y2(Co1−xFex)17 (0 ≤ x ≤ 0.3) compounds with the Th2Ni17 hexagonal structure were prepared with the purpose of tuning the EMDs. As x increases, the EMDs of the Y2(Co1−xFex)17 compounds change from the ab-plane (0 ≤ x < 0.0329) to the cone (0.0329 ≤ x ≤ 0.038) and then to the c-axis direction (0.038 < x ≤ 0.3). Furthermore, it was found that the extremely high cutoff frequencies of the uniaxial anisotropy materials give them considerably potential for microwave absorption applications above 10 GHz, despite their relatively low initial permeability compared to the planar anisotropic materials. By studying the high-frequency properties of Y2(Co1−xFex)17/paraffin composites, it is noted that uniaxial anisotropy compounds with x = 0.1 and x = 0.3 can possess higher permeability above 10 GHz as compared to both planar anisotropy and conical anisotropy compounds (x < 0.1) due to their high cutoff frequencies arising from large magnetocrystalline anisotropy fields. This can improve the impedance matching and thus lead to a better microwave absorption performance in the range of 10 to 40 GHz for materials with uniaxial anisotropy. Among all the compositions, the Y2(Co0.9Fe0.1)17/paraffin composite exhibits a minimum reflection loss (RL) of −50 dB at 6 GHz with a thickness of 2.5 mm and a wide qualified bandwidth (QB, RL < −10 dB) of 9.6 GHz at a center frequency of 30.3 GHz with a thickness of 0.6 mm, thus making it a promising candidate for MAMs above 10 GHz.