Magnetic and electronic properties of Eu₄Sr₄Ga₁₆Ge₃₀

G.T. Woods
J. Martin
M. Beekman
Raphaël P. Hermann
Fernande Grandjean
Veerle Keppens, University of Tennessee, Knoxville
O. Leupold
Gary J. Long
G.S. Nolas

Abstract

Magnetization, static and ac magnetic susceptibility, nuclear forward scattering, and electrical resistivity measurements have been performed on polycrystalline Eu₄Sr₄Ga₁₆Ge₃₀, 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 Eu₈Ga₁₆Ge₃₀ and Eu₆Sr₂Ga₁₆Ge₃₀. The ferromagnetic ordering of these Eu-containing clathrates is substantially altered by the incorporation of strontium, as compared to Eu₈Ga₁₆Ge₃₀. Ferromagnetism, accompanied by a relatively large negative magnetoresistance, is observed below 15 and 20 K in Eu4Sr4Ga16Ge30 and Eu6Sr2Ga16Ge30, respectively. An effective magnetic moment of 7.83 μB per Eu ion is observed above 30 K for Eu4Sr4Ga16Ge30, a moment which is close to the free-ion moment of 7.94 μB per europium(II) ion.