Highly Complex Magnetic Structures Resulting From Hierarchical Phase Separation in AlCo(Cr)FeNi High Entropy Alloys

TL;DR

This study investigates the complex magnetic structures in AlCo(Cr)FeNi high entropy alloys, revealing how hierarchical phase separation influences magnetic vortex formation and coercivity through advanced spatially-resolved analyses.

Contribution

It uncovers the relationship between hierarchical multi-phase structures and local magnetic behaviors in HEAs, highlighting the role of phase decomposition in magnetic vortex formation.

Findings

Hierarchical phase separation affects magnetic vortex states.

Magnetic vortex reversal contributes to coercivity.

Complex multi-phase structures influence magnetic properties.

Abstract

Magnetic high entropy alloys (HEAs) are a new category of high-performance magnetic materials, with multi-component concentrated compositions and complex multi-phase structures. Although there have been numerous reports of their interesting magnetic properties, there is very limited understanding about the interplay between their hierarchical multi-phase structures and their local magnetic structures. By employing high spatial resolution correlative magnetic, structural and chemical studies, we reveal the influence of a hierarchically decomposed B2 + A2 structure in an AlCo0.5Cr0.5FeNi HEA on the formation of magnetic vortex states within individual A2 (disordered BCC) precipitates, which are distributed in an ordered B2 matrix that is weakly ferromagnetic. Non-magnetic or weakly ferromagnetic B2 precipitates in large magnetic domains of the A2 phase, and strongly magnetic Fe-Co-rich interphase A2 regions, are also observed. These results provide important insight into the origin of coercivity in this HEA, which can be attributed to a complex magnetization process that includes the successive reversal of magnetic vortices.