Magnetic transitions and giant magnetocaloric effect in Eu$_{8}$Ga$_{16}$Ge$_{30 }$clathrates

Semiconductors with the clathrate hydrate crystal structure have demonstrated interesting physical properties that are directly related to the fact that ``guest'' atoms reside inside ``host'' polyhedra that are formed by other species. These materials are well known for their excellent thermoelectric properties. One of the interesting ``guests'' in the clathrate structure is europium. Since the magnetic moment of Eu is large and the Eu moments order at low temperatures in Eu$_{8}$Ga$_{16}$Ge$_{30}$ clathrates, these materials are expected to exhibit interesting magnetic and magnetocaloric properties. In this work, we report on the systematic studies of magnetic and magnetocaloric properties of Eu$_{8}$Ga$_{16}$Ge$_{30}$ clathrates. The magnetic entropy change was numerically calculated from the magnetization isotherms using the Maxwell relation and giant magnetocaloric effect (GMCE) was observed. Experimental results reveal a coherent correlation between the structure, magnetic property and the GMCE in Eu$_{8}$Ga$_{16}$Ge$_{30}$ clathrates. The low-field GMCE, in addition to the absence of thermal hysteresis and field hysteresis, makes this material an attractive candidate for active magnetic refrigeration at low temperatures.