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

TL;DR

This study explores how non-stoichiometry in HoB2-x particles affects their microstructure, phase composition, and magnetocaloric properties, revealing that Ho-rich compositions improve their suitability for magnetic refrigeration.

Contribution

It demonstrates that Ho-rich electrode rods produce particles with enhanced magnetocaloric properties and better mechanical characteristics despite impurity phases.

Findings

Ho-rich particles have increased HoB4 phase.

Magnetic entropy change is only slightly reduced despite impurities.

Ho phase improves mechanical properties of particles.

Abstract

We fabricate gas-atomized particles by inductively melting electrode rods of HoB2-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 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 HoB2.0 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 HoB2-x particles with more suitable properties as a magnetic refrigerant for magnetic refrigeration systems.