Effect of Non-Stoichiometry on Magnetocaloric Properties of HoB2 Gas-Atomized Particles

We fabricate gas-atomized particles by inductively melting electrode rods of HoB_2−x ( $x = -0.3$ , 0, 0.3, and 1.0) and investigate the effect of non-stoichiometry on the phase fraction, microstructure, and physical properties. Shifting the stoichiometric ratio of the electrode rod to the B (Ho)-rich side increases the HoB₄ (Ho) phase in the resulting atomized particles. Even if the atomized particles contain 15–20 weight percent (wt.%) of the impurity phase, the influence of which on the physical properties is less severe: the maximum value of the magnetic entropy change is only reduced by 10% compared to HoB_2.0 particles. We further find that the ductile Ho phase exists so as to fill the space between the brittle HoB₂ phases in the atomized particles, which may be beneficial to the mechanical properties of the particles. Our findings suggest that it would be better to use the Ho-rich electrode rods than the stoichiometric ones to produce HoB_2−x particles with more suitable properties as a magnetic refrigerant for magnetic refrigeration systems.