Gaudefroyite: a mineral with excellent magnetocaloric effect suitable for liquefying hydrogen

Gaudefroyite contains chains of edge-linked MnO₆ octahedra on a Kagomé lattice which results in magnetic frustration between the chains and overall spin-liquid behaviour below 9 K. Magnetization and specific heat measurements indicate very large entropy increases for temperatures of 10–30 K on removal of applied magnetic fields as low as 2 T. This is attributed to the degenerate magnetic ground states originating from the frustrated Kagomé lattice. Direct temperature change measurements confirm that the mineral has excellent low-field magnetocaloric properties suitable for refrigeration to produce liquid hydrogen.