Reactive single-step hot-pressing and magnetocaloric performance of polycrystalline Fe2Al1.15−xB2GexGax (x = 0, 0.05) MAB phases

Reactive single-step hot-pressing at 1473 K and 35 MPa for 4 h produces dense, bulk, near single-phase, low-cost, and low-criticality Fe2Al1.15B2 and Fe2Al1.1B2Ge0.05Ga0.05 MAB samples, showing second-order magnetic phase transition with favorable magnetocaloric properties around room temperature. The magnetic as well as the magnetocaloric properties can be tailored upon Ge and Ga doping, leading to an increase in the Curie temperature TC and the spontaneous magnetization mS. The maximum isothermal entropy change ΔsT,max of hot-pressed Fe2Al1.15B2 in magnetic field changes of 2 and 5 T amounts to 2.5 and 5 J(kgK)−1 at 287.5 K and increases by Ge and Ga addition to 3.1 and 6.2 J(kgK)−1 at 306.5 K, respectively. The directly measured maximum adiabatic temperature change ΔTad,max is improved by composition modification from 0.9 to 1.1 K in magnetic field changes of 1.93 T. Overall, we demonstrate that hot-pressing provides a much faster, more scalable, and processing costs reducing alternative compared to conventional synthesis routes to produce heat exchangers for magnetic cooling devices. Therefore, our criticality assessment shows that hot-pressed Fe-based MAB phases provide a promising compromise of material and processing costs, criticality, and magnetocaloric performance, demonstrating the potential for low-cost and low-criticality magnetocaloric applications around room temperature.