Sustainable Magnets with Strong Anisotropy

High magnetic anisotropy materials have critical applications in numerous technology sectors, from magnetic recording to high energy-density permanent magnets that are widely used in consumer electronics and clean energy technologies. The dependence of these technologies on rare-earth elements is a longstanding concern for sustainability due to their susceptibility to market volatility, supply chain issues, and the environmental toll from mining. While the search for new rare-earth-free high anisotropy materials has exhausted much of the pool of binary and ternary alloy compositions, entropy-stabilization in high entropy materials (HEMs) affords a vast number of unique and unexplored electronic structures potentially favorable to high magnetic anisotropy. Conventional HEAs exhibit uniform chemical disorder and cubic crystal structures, whereas long-range chemical order and low-symmetry crystal structures play important roles in magnetic anisotropy. Here we present on the design and fabrication strategies to realize magnetic HEMs with intermetallic sublattices and uniaxial symmetry, and explorations of their magnetic properties throughout the composition space [1,2]. We start by demonstrating a fabrication approach based on sputtering and rapid thermal annealing (RTA) in FeCoNiMnCu thin films, which show an almost 40-fold increase in coercivity from the as-grown state. Next, inclusion of Pt in the film leads to ordering of a single L1₀ high entropy intermetallic phase after RTA, along with development of a large perpendicular anisotropy and 3-orders of magnitude increase in coercivity [1,2]. Finally, we explore the composition space of C16 phase 3d transition metal borides using a combinatorial approach, leading to discovery of a novel high anisotropy composition beyond the binary and ternary borides. These explorations represent a potentially disruptive concept in using HEMs as a whole new way of achieving sustainable, strong magnets.

This work has been supported in part by the NSF (ECCS-2151809, DMR-1828420), 5E Advanced Materials, NIST (70NANB22H101/MML22-1014), and the Pittsburgh Super-computing Center through the ACCESS Program.

1. W. B. Beeson, D. Bista, H.R. Zhang, S. Krylyuk, A. Davydov, G. Yin, and Kai Liu, “Single-Phase L1₀-Ordered High Entropy Thin Films with High Magnetic Anisotropy”, Adv. Sci. 11, 2308574 (2024).
2. D. Bista, W. B. Beeson, T. Sengupta, J. Jackson, S. N. Khanna, Kai Liu, and Gen Yin, “Fast ab initio design of high-entropy magnetic thin films”, Phys. Rev. Mater. submitted; arXiv: 2404.18283 (2024).