Anisotropy-Driven Discovery of Rare-Earth-Free Magnets in Mo₂FeB₂-Type Borides

Multifunctional materials are critically important for modern technologies. Magnets, especially those relevant to spintronic applications, are essential for energy-efficient data processing and advanced magnetic devices, while high-strength materials provide excellent mechanical and thermal stability. Mo₂FeB₂-type materials are well established for their superior strength and thermal properties, yet their magnetic behavior has remained largely theoretical, dominated by antiferromagnets and, more recently, predicted altermagnets. Building on our recent report of spin-glass phases exhibiting large anisotropy, we have discovered Mo₂FeB₂-type high-temperature ferromagnets: Mn-rich MoMn₂B₂ and WMn₂B₂. These compounds exhibit magnetic ordering above room temperature, with Curie temperatures (and Weiss constants) of 400 K (θ = 229 K) and 380 K (θ = +154 K), respectively. Notably, rare-earth-free WMn₂B₂ displays enhanced coercivity with an intrinsic coercivity of 67.6 kA m^-1 at 5 K, supported by DFT calculations revealing a large in-plane magnetocrystalline anisotropy energy of +0.27 meV/f.u., driven by the strong spin-orbit coupling of tungsten. These findings show that Mn-rich Mo₂FeB₂-type borides are promising rare-earth-free permanent magnet candidates that combine high-temperature ferromagnetism, enhanced magnetic anisotropy, and excellent structural stability.