High frequency magnetic behavior of FeCoNiMnxAl1−x high-entropy alloys regulated by ferromagnetic transformation

Fe-Co-Ni-Al high entropy alloys (HEAs) with lower coercivity (Hc) and high permeability are considered as a new generation of candidates for microwave absorbing materials. Expecting to obtain higher saturation magnetization (Ms) and high frequency permeability, we designed a series of FeCoNiMnxAl1−x (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) HEAs, and first principles calculations were used to explore the spin state and magnetic changes of Mn with different Al content under the ferromagnetic transition of Mn. Firstly, the face-centered-cubic (FCC) and body-centered-cubic (BCC) phases with almost equal content were determined by experiments. The atomic models of HEAs were successfully established using the obtained crystal structure information and the spin states and magnetic moments of elements in HEAs with different Mn content were calculated. Due to the magnetic moments of ferromagnetic elements and the anti-ferromagnetic to ferromagnetic transformation of Mn elements, when Mn content is 0.2, the average magnetic moment reached 0.85/atom. The experimental results authenticate that FeCoNiMn0.2Al0.8 has the highest Ms of 95.0 emu/g. Higher Ms is favorable for HEAs to exhibit favorable high frequency magnetic properties, the maximum value of μ′ is 2.341, and that of μ″ is 0.823 in GHz frequency. This work illustrates the importance of the ferromagnetic transformation of Mn in HEAs for regulating high frequency magnetic properties and shows the guiding significance for predicting the magnetic properties of absorbing materials via using first principles calculations.