Zero thermal expansion and magnetocaloric effect in B doped Fe2(Hf,Ta) Laves phase compounds

Abstract

Materials with zero thermal expansion (ZTE) or negative thermal expansion (NTE) are critical for precision applications. Magnetocaloric materials exhibiting a strong spin-lattice coupling often undergo lattice changes near a magnetic transition, offering a route to ZTE behavior via magnetoelastic effects. This study examines the effect of Boron doping on the magnetoelastic transition, thermal expansion and magnetocaloric properties in Fe1.98Hf0.85Ta0.15B ₓ (x = 0.00, 0.01, 0.02, 0.03, 0.04) Laves phase alloys. Boron doping enhances hardness and increases the field sensitivity of the transition temperature. The second-order transition in the undoped alloy evolves into a first-order ferromagnetic-antiferromagnetic transition upon doping. First-principles calculations show that B occupies the 2 a sites, modifying the Fe-Hf 3 d -5 d hybridization and strengthening the spin-lattice coupling. In the Fe1.98 Hf0.85Ta0.15B0.01 alloy a near-zero thermal expansion with a coefficient of −0.17 ppm/K is observed in a temperature range of 133–213 K below the magnetoelastic transition at T t = 266 K, which is ascribed to the enhanced magnetoelastic transition by light-element doping with B. Our findings highlight a promising strategy to optimize the ZTE behavior through targeted light-element doping in magnetocaloric Laves phase systems.