Influence of the Fe/Co ratio on the structural and magnetic properties of FeCoMnAlSi high-entropy alloys with varied Mn content

In this study, the effects of Fe:Co ratio on the structure and magnetic properties of high-entropy alloys (HEAs) with different Mn contents (5% and 15%) are investigated by combining experimental and theoretical approaches. The alloys mainly show bcc and $B2$ coexisting structures, and the change of Mn content has less effect on the structure. The coercivity of all alloys is less than 10 Oe, showing soft magnetic properties, and the highest saturation magnetization of $195.5\phantom{\rule{0.28em}{0ex}}\mathrm{emu}\phantom{\rule{0.16em}{0ex}}{\mathrm{g}}^{\ensuremath{-}1}$ is obtained at the Fe:Co ratio of 2:1 for alloy with 5% Mn, and the highest saturation magnetization of $182.8\phantom{\rule{0.28em}{0ex}}\mathrm{emu}\phantom{\rule{0.16em}{0ex}}{\mathrm{g}}^{\ensuremath{-}1}$ is obtained at the Fe:Co ratio of 1:1 for alloy with 15% Mn. Density-functional theory (DFT) calculations revealed the magnetic moment distribution of each element, with the results basically consistent with the experiments. The research results indicated that the Mn atomic magnetic moment is more sensitive to the variation in the Fe:Co ratio. Increasing the Mn content decreases the atomic magnetic moments of Fe and Co, but the effect on Fe is greater, indicating a stronger antiferromagnetic coupling between Fe and Mn. At lower Mn content, the average magnetic moment of Mn is higher, revealing the enhancement or suppression of magnetism due to the ferromagnetic/antiferromagnetic interactions between Mn and Mn or others. This study provides an important theoretical basis for the design of Mn-containing HEAs with optimized magnetic properties.