A mechanically strong and ductile soft magnet with extremely low coercivity

TLDR

Soft magnetic materials are essential for low‑loss electrical devices, yet reducing coercivity while maintaining high strength and ductility remains a fundamental design challenge because strengthening mechanisms often pin magnetic domains. The study proposes a strategy to simultaneously achieve low coercivity and high mechanical performance in soft magnetic alloys. A Fe‑Co‑Ni‑Ta‑Al multicomponent alloy was engineered with a ferromagnetic matrix and ~55 % volume of ~91‑nm paramagnetic coherent nanoparticles that hinder dislocation motion while keeping the interaction volume below the domain‑wall width to prevent coercivity increase. The alloy exhibits a tensile strength of 1336 MPa at 54 % elongation, an exceptionally low coercivity of 78 A/m (<1 Oe), a moderate saturation magnetization of 100 Am²/kg, and a high electrical resistivity of 103 μΩ·cm.

Abstract

Soft magnetic materials (SMMs) serve in electrical applications and sustainable energy supply, allowing magnetic flux variation in response to changes in applied magnetic field, at low energy loss1. The electrification of transport, households and manufacturing leads to an increase in energy consumption due to hysteresis losses2. Therefore, minimizing coercivity, which scales these losses, is crucial3. Yet, meeting this target alone is not enough: SMMs in electrical engines 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 an approach to overcome this dilemma. We have designed a Fe-Co-Ni-Ta-Al multicomponent alloy with ferromagnetic matrix and paramagnetic coherent nanoparticles (~91 nm size, ~55% volume fraction). They impede dislocation motion, enhancing strength and ductility. Their small size, low coherency and small magnetostatic energy create an interaction volume below the magnetic domain wall width, leading to minimal domain wall pinning, thus maintaining the soft magnetic properties. The alloy has a tensile strength of 1336 MPa at 54% tensile elongation, extremely low coercivity of 78 A/m (<1 Oe), moderate saturation magnetization of 100 Am2/kg, and high electrical resistivity of 103 {\mu}{\Omega} u Ohm cm.