Complex Magnetism of Single-Crystalline AlCoCrFeNi Nanostructured High-Entropy Alloy

We have investigated magnetism of the Al28Co20Cr11Fe15Ni26 single-crystalline high-entropy alloy. The material is nanostructured, composed of a B2 matrix with dispersed spherical-like A2 nanoparticles of average diameter 64 nm. The magnetism was studied from 2 to 400 K via direct-current magnetization, hysteresis curves, alternating-current magnetic susceptibility, and thermoremanent magnetization time decay, to determine the magnetic state that develops in this highly structurally and chemically inhomogeneous material. The results reveal that the Cr-free B2 matrix of composition Al28Co25Fe15Ni32 forms a disordered ferromagnetic (FM) state that undergoes an FM transition at TC≈ 390 K. The Al- and Ni-free A2 nanoparticles of average composition Co19Cr56Fe25 adopt a core-shell structure, where the shells of about 2 nm thickness are CoFe enriched. While the shells are FM, the nanoparticle cores are asperomagnetic, classifying into the broad class of spin glasses. Asperomagnetism develops below 15 K and exhibits broken-ergodicity phenomena, typical of magnetically frustrated systems.