Magnetocaloric effect in the Laves-phaseHo1−xDyxAl2family in high magnetic fields

Hydrogen has the largest gravimetric energy density among all chemical fuels. At the same time, the density of gaseous ${\mathrm{H}}₂$ is extremely low, which makes its compression to high pressures, liquefaction, or solid-state storage necessary for transport purposes. Liquid hydrogen ($\mathrm{L}{\mathrm{H}}₂$) can be transported in a dewar under atmospheric pressure, but this requires energy-intensive cooling down to $20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Magnetocaloric materials have great potential to revolutionize gas liquefaction to make $\mathrm{L}{\mathrm{H}}₂$ more competitive as fuel. In this paper, we investigate a series of Laves-phase materials regarding their structural, magnetic, and magnetocaloric properties in high magnetic fields. The three compounds $\mathrm{Ho}{\mathrm{Al}}₂$, ${\mathrm{Ho}}_0.5{\mathrm{Dy}}_0.5{\mathrm{Al}}₂$, and $\mathrm{Dy}{\mathrm{Al}}₂$ are suited for building a stack for cooling from liquid-nitrogen temperature ($77\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) down to the boiling point of hydrogen at $20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. This is evident from our direct measurements of the adiabatic temperature change in pulsed magnetic fields, which we compare with calorimetric data measured in a static field. With this methodology, we are now able to study the suitability of magnetocaloric materials down to low temperatures up to the highest magnetic fields of 50 T.