Charge-Ordered State and Low-Dimensional Magnetic Fluctuations in Yb5Ge4 Single Crystal

We have successfully grown single crystals of Yb5Ge4 and performed measurements of magnetization, specific heat, electrical resistivity, and Hall effect. Yb5Ge4 is ordered antiferromagnetically at TN = 1.7 K with broad anomalies appearing just above TN in the magnetic susceptibility and specific heat curves. An evaluation of the effective magnetic moments and magnetic entropy suggest that the ratio of Yb valences in this compound is Yb3+:Yb2+=2:3, as also supported by a hard X-ray photoemission spectrum analysis. To study the relations between the physical properties and Yb valence states, we applied an X-ray diffraction anomalous fine structure (DAFS). The obtained DAFS spectra can be interpreted as the formation of a charge-ordered state rather than a valence-fluctuating state, implying the existence of a low-dimensional zigzag chain constructed through magnetic Yb3+ ions. The characteristic features in magnetization and specific heat measurements are most likely due to strong magnetic fluctuations arising from the low-dimensional arrangement of magnetic Yb3+ ions.