Magnetic and electronic properties of Eu4 Sr4 Ga16 Ge30

Magnetization, static and ac magnetic susceptibility, nuclear forward scattering, and electrical resistivity measurements have been performed on polycrystalline Eu4 Sr4 Ga16 Ge30, a type I clathrate that has divalent strontium and europium ions encapsulated within a Ga-Ge framework. These data are compared with those of type I clathrates Eu8 Ga16 Ge30 and Eu6 Sr2 Ga16 Ge30. The ferromagnetic ordering of these Eu-containing clathrates is substantially altered by the incorporation of strontium, as compared to Eu8 Ga16 Ge30. Ferromagnetism, accompanied by a relatively large negative magnetoresistance, is observed below 15 and 20 K in Eu4 Sr4 Ga16 Ge30 and Eu6 Sr2 Ga16 Ge30, respectively. An effective magnetic moment of 7.83 μB per Eu ion is observed above 30 K for Eu4 Sr4 Ga16 Ge30, a moment which is close to the free-ion moment of 7.94 μB per europium(II) ion.