Suppression of impurity phases and the study of magnetic and magnetocaloric properties of Ho2Co2Al intermetallic compound

The R2Co2Al compounds (R = Tb, Dy, Ho, Er, Tm) are known to contain RCoAl-type impurity. In order to suppress the impurity phase in Ho2Co2Al intermetallic compound, nonstoichiometric samples with excess rare-earth Ho were prepared and annealed. Structural analysis indicates that annealed nonstoichiometric Ho42Co40Al20 sample, with 2 at% excess Ho, comprises the Ho2Co2Al phase and minor traces of Ho2O3 oxide. Magnetic and magnetocaloric properties of the sample have been studied in detail. The alloy undergoes three phase transitions at 9 K, 21 K and 30 K. The multiple transitions and broadening effect of second-order phase transitions (SOT) on peak magnetic entropy change (−ΔSM), result in good refrigerant capacities (RCareas) of 136.9 and 437 J/kg under field changes (ΔH) of 2 and 5 T, respectively. These values of RCarea and their corresponding large −ΔSM peak magnitudes of 9.1 and 18.4 J/kg K under ΔH = 2 and 5 T, respectively, make Ho2Co2Al a promising and competitively good candidate magnetic refrigerant for low temperature cooling applications such as liquefaction of hydrogen gas.