We performed electrical resistivity ρ, magnetization M and specific heat C measurements on single crystals of a type-I clathrate compound Eu 8Ga16Ge30, where the guest magnetic ions of Eu2+ in the tetrakaidecahedral cages are rattling among off-center positions. The jump of C at the Curie temperature TC is only one third of the value expected for a uniform ferromagnet with S=7/2 from the mean-field theory. Both ρ(T) and dM(T)/dT show broad humps at T*=20-24 K, where C(T) has no anomaly. With increasing magnetic fields to 5 T, the T* in ρ(T) shifts to 40 K. These observations indicate a crossover from a modulated structure to a uniform one on cooling through T*.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)