EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

A good soft magnetic material that exhibit properties applicable for commercial soft magnets used in transformers, motors, generators and other electromagnetic machinery should show minimal magnetization hysteresis, low magnetostriction, high saturation magnetic polarization, the highest possible permeability and large electrical resistivity to reduce remanence and losses in static and AC application. Examples of widely used commercial alloys at frequencies from DC up to the audio range (100 Hz–100 kHz) are non-oriented and grainoriented silicon electrical steels, V-permendur, Hypernik, Mumetal, Supermalloy, Metglas 2628SC and Finmet, which possess negligible coercivities. For this presentations, the authors report on the discovery of a perfect magnetically soft high-entropy alloy of composition FeCoNiPdCu, which performs comparably to the best commercial soft magnets. Properly heat-treated FeCoNiPdCu develops nanostructure that can be viewed as a two-phase bulk nanocomposite of randomly intermixed FeCoNi magnetic domains and PdCu nonmagnetic “spacers”, both of 2–5 nm cross dimensions. Due to the nanometric size, the FeCoNi domains are magnetically single-domain particles, and since the particles are exchange-coupled across the boundaries, exchange averaging of magnetic anisotropy takes place, resulting in an almost vanishing coercive field and excellent magnetic softness. The formation of a two-phase nanostructure favourable for the exchange averaging of magnetic anisotropy is a consequence of specific values of the binary mixing enthalpies for the chosen elements. Though high-entropy alloys are generally considered to be random solid solutions of multiple elements on a topologically ordered crystal lattice, clustering of the atoms into preferential chemical environments on a nanoscale essentially determines their magnetic properties (P. Koželj et al., Advanced Engineering Materials 2019: 1801055).