  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
Fe$_2$Al$_{1.15}$B$_2$ and Fe$_2$Al$_{1.1}$B$_2$Ge$_{0.05}$Ga$_{0.05}$ MAB
samples, showing a second-order magnetic phase transition with favorable
magnetocaloric properties around room temperature. The magnetic as well as
magnetocaloric properties can be tailored upon Ge and Ga doping, leading to an
increase of Curie temperature $T_C$ and spontaneous magnetization $m_S$. The
maximum isothermal entropy change $\Delta s_{T,max}$ of hot-pressed
Fe$_2$Al$_{1.15}$B$_2$ 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 $\Delta T_{ad,max}$ is improved by the 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 cost 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 cost, criticality and
magnetocaloric performance, demonstrating the potential for low-cost and
low-criticality magnetocaloric applications around room temperature.
