Novel CoFeAlMn high-entropy alloys with excellentsoft magnetic properties and high thermal stability

Abstract

High-entropy alloys (HEAs), which are composed of 3d transition metals such as Fe, Co, and Ni, exhibit an exceptional combination of magnetic and other properties; however, the addition of non-ferromagnetic elements always negatively affects the saturation magnetization strength (Ms). Co4Fe2AlxMny alloys were designed and investigated in this study to develop a novel HEA with excellent soft magnetic properties. The Co4Fe2Al1.5Mn1.5 HEA possesses the highest Ms of 161.3 emu g–1 thus far reported for magnetic HEAs, a low coercivity of 1.9 Oe, a high electrical resistivity of 173 μΩ cm, a superior thermal stability up to 600 °C, which originates from the novel microstructure of B2 nanoparticles distributed in a DO3 matrix phase, and the crucial transition of Mn from antiferromagnetism to ferromagnetism with the assistance of Al. The Co4Fe2Al1.5Mn1.5 HEA was selected to produce micron-sized powder and soft magnetic powder cores (SMPCs) for application in the exploration field. The SMPCs exhibit a high stable effective permeability of 35.9 up to 1 MHz, low core loss of 38.1 mW cm–3 (@100 kHz, 20 mT), and an excellent direct current (DC) bias performance of 87.7% at 100 Oe. This study paves the way for the development of soft magnetic HEAs with promising applications as magnetic functional materials.