Magnetocaloric effect in the Laves-phase Ho_1−xDy_xAl₂ family in high magnetic fields

Hydrogen has the largest gravimetric energy density among all chemical fuels. At the same time, the density of gaseous H₂ is extremely low, which makes its compression to high pressures, liquefaction, or solid-state storage necessary for transport purposes. Liquid hydrogen (LH₂) can be transported in a dewar under atmospheric pressure, but this requires energy-intensive cooling down to 20 K. Magnetocaloric materials have great potential to revolutionize gas liquefaction to make LH₂ 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 HoAl₂, Ho_0.5Dy_0.5Al₂, and DyAl₂ are suited for building a stack for cooling from liquid-nitrogen temperature (77 K) down to the boiling point of hydrogen at 20 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.