A mechanically strong and ductile soft magnet with ultralow coercivity

Soft magnetic materials (SMMs) are indispensable components in electrified applications and sustainable energy supply, allowing permanent magnetic flux variations in response to high frequency changes of the applied magnetic field, at lowest possible energy loss1. The global trend towards electrification of transport, households and manufacturing leads to a massive increase in energy consumption due to hysteresis losses2. Therefore, minimizing coercivity, which scales the losses in SMMs, is crucial3. Yet, meeting this target alone is not enough: SMMs used for instance in vehicles and planes must withstand severe mechanical loads, i.e., the alloys need high strength and ductility4. This is a fundamental design challenge, as most methods that enhance strength introduce stress fields that can pin magnetic domains, thus increasing coercivity and hysteretic losses5. Here, we introduce a new approach to overcome this dilemma. We have designed a Fe-Co-Ni-Ta-Al multicomponent alloy with ferromagnetic matrix and paramagnetic coherent nanoparticles of well-controlled size (~91 nm) and high volume fraction (55%). They impede dislocation motion, enhancing strength and ductility. Yet, their small size, low coherency stress and small magnetostatic energy create an interaction volume below the magnetic domain wall width, leading to minimal domain wall pinning, thus maintaining the material’s soft magnetic properties. The new material exhibits an excellent combination of mechanical and magnetic properties outperforming other multicomponent alloys and conventional SMMs. It has a tensile strength of ~1336 MPa at 54% tensile elongation, an extremely low coercivity of ~78 A/m (<1 Oe) and a saturation magnetization of ~100 Am2/kg. The work opens new perspectives on developing magnetically soft and mechanically strong and ductile materials for the sustainable electrification of industry and society.