  Recently, a massive magnetocaloric effect near the liquefaction temperature
of hydrogen has been reported in the ferromagnetic material HoB$_{2}$. Here we
investigate the effects of Dy substitution in the magnetocaloric properties of
Ho$_{1-x}$Dy$_{x}$B$_{2}$ alloys ($\textit{x}$ = 0, 0.3, 0.5, 0.7, 1.0). We
find that the Curie temperature ($\textit{T}$$_{C}$) gradually increases upon
Dy substitution, while the magnitude of the magnetic entropy change |$\Delta
\textit{S}_{M}$| at $\textit{T}$ = $\textit{T}_{C}$ decreases from 0.35 to 0.15
J cm$^{-3}$ K$^{-1}$ for a field change of 5 T. Due to the presence of two
magnetic transitions in these alloys, despite the change in the peak magnitude
of |$\Delta \textit{S}_{M}$|, the refrigerant capacity ($\textit{RC}$) and
refrigerant cooling power ($\textit{RCP}$) remains almost constant in all
doping range, which as large as 5.5 J cm$^{-3}$ and 7.0 J cm$^{-3}$ for a field
change of 5 T. These results imply that this series of alloys could be an
exciting candidate for magnetic refrigeration in the temperature range between
10-50 K.

Materials Science