Magnetocaloric effect and refrigerant capacity in Eu$_{8}$Ga$_{16}$Ge$_{30}$ clathrates and Eu$_{8}$Ga$_{16}$Ge$_{30}$-EuO composites

Eu$_{8}$Ga$_{16}$Ge$_{30}$ clathrates are widely known for their excellent thermoelectric properties. Recently, we have discovered the giant magnetocaloric effect (MCE) in Eu$_{8}$Ga$_{16}$Ge$_{30}$ type-VIII clathrates. The tunable MCE and refrigerant capacity (RC) have also been achieved in Eu$_{8}$Ga$_{16}$Ge$_{30 }$type-I clathrates by partial substitution of Eu with non-magnetic Sr. As an interesting host matrix the type-I clathrates are combined with EuO at different portions (80{\%}/20{\%}, 70{\%}/30{\%}, 65{\%}/35{\%}, 60{\%}/40{\%}, 40{\%}/60{\%}) for making novel composites with enhanced RC over a tunable temperature range (10-100K). We have achieved a very large RC of 794 J/kg at 5T over a 70K in the clathrate type I -- EuO (40{\%}/60{\%}) composite, which is the largest value ever achieved among the existing materials for magnetic refrigeration around 70K. This composite is very attractive for magnetic refrigeration for nitrogen liquefaction. A new potential of using the type VIII clathrate -- EuO composite (50{\%}-50{\%}) to produce refrigeration in two different temperature ranges has been proposed.