Highly Complex Magnetic Microstructures in Hierarchically Phase Separated AlCo(Cr)FeNi High-entropy Alloys

The hierarchical microstructures of high-entropy alloys (HEAs) can result in highly complex magnetic textures and properties. Here, we use high spatial resolution correlative magnetic, structural and chemical imaging to investigate magnetic textures in phase separated AlCoxCr1 – xFeNi (x = 0.5 and 1) HEAs. The AlCoFeNi HEA, which contains nm-sized A2 precipitates in a B2 matrix, supports large magnetic domains with small-angle magnetization variations. In contrast, the AlCo(Cr)FeNi HEA, which undergoes hierarchical phase separation, contains an unexpected distribution of magnetic vortices within individual A2 precipitates in a weakly ferromagnetic B2 host, in addition to weakly ferromagnetic or nonmagnetic B2 precipitates in large magnetic domains of the A2 phase, as well as Fe-Co-rich inter-phase A2 regions that have strong magnetization. The coercivity is attributed to a complicated magnetization reversal process, which includes the successive reversal of the magnetic vortices. These results provide important insight for the rational design of HEAs with unique and tailored magnetic properties.