Magnetic and transport properties of single-crystal Yb ₃Cu ₄Ge ₄

The magnetic and transport properties of single-crystal Yb ₃Cu ₄Ge ₄ with the Gd ₃Cu ₄Ge ₄-type orthorhombic structure are presented. Magnetization along the b-axis at 2 K saturates to 2.8 ^μB/Yb at 3 kOe, while that along the a- and c-axes at 2 K are gradually increasing to the value of 1.5 ^μB/Yb and 0.39 ^μB/Yb at 50 kOe, respectively. The electrical resistivity within the ab-plane shows a metallic behavior in contrast to a broad maximum at around 30 K for that along the c-axis. Each resistivity for the principal axis suddenly decreases below 8 K. The specific heat shows a λ-type sharp peak at 7.8 K. The electronic specific heat coefficient is estimated to be 29.4 mJ/mol Yb K ² by fitting the magnetic part of the specific heat below 3 K. The magnetic entropy released up to T _C is 68% of that of R ln 2, expected for the doublet ground state. It is revealed that Yb ₃Cu ₄Ge ₄ is categorized to a weak heavy-fermion system showing a ferromagnetic transition at 7.8 K with uniaxial anisotropy along the b-axis.