The magnetocaloric effect of the lanthanide fluorides: Using polarized neutron scattering to probe a magnetocaloric suitable for hydrogen liquefaction

This work reports the competitive magnetocaloric effect of some simple lanthanide fluoride materials with cations with high magnetic anisotropy. Of these, HoF3 is particularly promising due to exhibiting a high magnetocaloric entropy change under modest applied fields at higher temperatures, which only decreases modestly with temperature such that it has the potential for cooling for hydrogen liquefaction. Spin-polarized neutron spectroscopy indicates that its promising conventional magnetocaloric effect is likely due to the presence of ferromagnetic fluctuations of highly anisotropic magnetic moments, while its singlet electronic ground state and low-temperature magnetic ordering lead to a decrease in its magnetocaloric performance below 4 K.