The FeCoNi(CuAl)_0.8 high-entropy alloy (HEA) consists of both face-centered cubic (FCC) phase and body-centered cubic (BCC) phase which allows for a fine tuning of the magnetic properties by controlling the concentration, morphology, and distribution of each phase. In this work, we report the effect of Ho addition on the microstructure, magnetic domains, and alternating current (AC) magnetic properties. FeCoNi(CuAl)_0.8Ho_0.05 (x = 0.05) HEA exhibits the optimum AC magnetic property with the minimum AC coercivity, hysteresis loss, eddy current loss and total loss among samples studied at both 50 Hz and 950 Hz. Ho addition increases the volume fraction of BCC phase. SEM-EDX results show that Cu and Ho elements are aggregated together at boundaries in Ho-containing alloys. Magnetic domain structure shows that stripe domains are observed in FCC phase and BCC phase with different domain width. Finely spaced domain in BCC phase leads to low eddy current loss. No domain pattern at boundaries is observed indicating that boundaries can hinder motion of domain resulting in an increase of the energy loss. Our findings provide a valid approach toward optimizing the desired physical properties of HEA magnets by adding a small fraction of rare earth element.

FeCoNi（CuAl）_0.8高熵合金（HEA）由面心立方（FCC）相和体心立方（BCC）相组成，可通过控制浓度，形貌，和每个阶段的分布。在这项工作中，我们报告了Ho添加对微观结构，磁畴和交流（AC）磁性能的影响。FeCoNi（CuAl）_0.8 Ho _0.05（x = 0.05）在50 Hz和950 Hz下研究的样品中，HEA表现出最佳的交流磁性能，同时具有最小的交流矫顽力，磁滞损耗，涡流损耗和总损耗。Ho的添加增加了BCC相的体积分数。SEM-EDX结果表明，Cu和Ho元素在含Ho合金的边界处聚集在一起。磁畴结构表明，在FCC相和BCC相中观察到具有不同畴宽的条状畴。BCC相中的微调磁畴可降低涡流损耗。在边界处未观察到畴图案，表明边界会阻碍畴的运动，从而导致能量损失的增加。我们的发现通过添加一小部分稀土元素，为优化HEA磁体的理想物理性能提供了一种有效的方法。