Zero‐Magnetostriction Magnetically Soft High‐Entropy Alloys in the AlCoFeNiCu x ( x  = 0.6–3.0) System for Supersilent Applications

Searching for materials that possess a combination of excellent magnetic softness and vanishing magnetostriction, the ferromagnetic high‐entropy alloy (HEA) system AlCoFeNiCu x ( x = 0.6–3.0) is investigated. Superior magnetostriction and magnetic softness parameters are obtained for the composition AlCoFeNiCu 2.0 , which shows zero magnetostriction, λ s = 0, low coercivity H c ≈ 650 A m −1 and substantial saturation magnetic polarization of J s ≈ 0.55 T. The parameters of other AlCoFeNiCu x compositions in the range x = 2.0–3.0 are only slightly different, so that the entire set of the AlCoFeNiCu x HEAs in that Cu content range can be classified as magnetically soft and vanishing‐magnetostriction alloys. The alloys develop a multiphase (up to three phases) composite microstructure that is further nanostructured on the 10 nm scale. Magnetic softness of the alloys originates from the exchange‐averaging of magnetic anisotropy, while vanishing magnetostriction coefficient of the AlCoFeNiCu 2.0 alloy results from its three‐phase microstructure, where the magnetostrictions of different signs exactly compensate each other at particular volume fractions. The AlCoFeNiCu x ( x = 2.0–3.0) HEAs are expected to find applications as supersilent (inaudible to a human ear) materials for transformers, magnetocaloric coolers, and other “humming” electromagnetic machinery.