Zero-Magnetostriction Magnetically Soft High-Entropy Alloys in the AlCoFeNiCux (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 AlCoFeNiCux (x = 0.6-3.0) is investigated. Superior magnetostriction and magnetic softness parameters are obtained for the composition AlCoFeNiCu2.0, which shows zero magnetostriction, lambda(s) = 0, low coercivity H-c approximate to 650 A m(-1) and substantial saturation magnetic polarization of J(s) approximate to 0.55 T. The parameters of other AlCoFeNiCux compositions in the range x = 2.0-3.0 are only slightly different, so that the entire set of the AlCoFeNiCux 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 AlCoFeNiCu2.0 alloy results from its three-phase microstructure, where the magnetostrictions of different signs exactly compensate each other at particular volume fractions. The AlCoFeNiCux (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.