Magnetic and Transport Properties of Single-Crystal YbPtGe

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The magnetic and transport properties of single-crystal YbPtGe with the TiNiSi-type orthorhombic structure are presented. It is revealed that YbPtGe is a ferromagnet with $T_{\text{C}} = 5.4$ K. Although both of its paramagnetic and ferromagnetic states show uniaxial anisotropy, its easy axis changes from the $a$-axis in the paramagnetic state to the $c$-axis below $T_{\text{C}}$. Magnetizations at 2 K along the $a$-, $b$-, and $c$-axes saturate to constant values of 1.5 $\mu_{\text{B}}$ for 6 kOe, 0.55 $\mu_{\text{B}}$ for 2 kOe, and 1.1 $\mu_{\text{B}}$ for 1 kOe, respectively. The magnetic contribution to the specific heat shows a Schottky anomaly centered at 90 K due to the crystalline electric field (CEF) effect that splits the eight-hold $J$-multiplet of the Yb3+ ion into four doublets. The Sommerfeld coefficient $\gamma$ is estimated to be 209 mJ/(mol$\cdot$K2) below $T_{\text{C}}$. The magnetic entropy released up to $T_{\text{C}}$ is 52% of that of $R\ln 2$, expected for the doublet ground state. Therefore, YbPtGe is a middle-classed heavy-fermion compound with a ferromagnetic transition.
2009-10-15