Low Temperature Properties of Ternary Magnetic Rare Earth Transition Metal Germanides with the SCANDIUM(5)COBALT(4)GERMANIUM(10) - Structure.

DC resistivity, dc magnetization, and specific heat of eight Sc_5Co_4 Ge_{10}-type crystal structure compounds R_5T _4Ge_{10} for R = Dy, Ho, Er, Tm, and T = Rh and Ir are presented. The resistivity, single crystal magnetization, and specific heat results show that in all those compounds, the magnetic moments order antiferromagnetically in the c direction at low temperature. However, in the Er and Tm compounds, the magnetizations along x-y hard directions do not show any anomalies above 2.0 K. This suggests that the ordered Er and Tm ions, which have positive quadrupole coefficients alpha_{rm j}, interact with a crystal field that has an electronic potential valley along the c axis. The fitting of the hard axis magnetizations to Curie-Weiss law suggests that the resulting antiferromagnetic-like theta reflects the strength of the crystal field torque on the magnetic moments rather than the strength of antiferromagnetic exchange.