Magnetic And Transport Properties Of The Narrow-Gap Semiconductor Yb5si4

We report the synthesis and basic properties of the binary compound Yb5Si4. In this compound, Yb ions occupy three different crystallographic sites, the multiplicity of which is represented by Ybl : Yb2 : Yb3 = 1 : 2 : 2. The estimated effective magnetic moment and magnetic entropy can be explained by the proportion of Yb valence states, Yb3+ : Yb2+ = 2 : 3. This result suggests the possibility that Yb3+ ions occupy either Yb2 or Yb3 site. Yb5Si4 undergoes an antiferromagnetic transition at T-N = 1.7 K. The extended high temperature tail in the temperature dependence of the specific heat just above T-N has been observed. Yb5Si4 also exhibits the broad maximum peak around 2.3 K in the magnetic susceptibility, corresponding to the specific heat anomaly. We propose that these anomalies are possible to originate from magnetic fluctuations caused by low-dimensional Yb3+ networks. Electrical resistivity measurements on Yb5Si4 reveal semiconducting behavior at all temperatures. The small energy gap Delta = 430 K has been obtained at room temperature estimated by the thermal activation model. The energy gap gradually decreases with decreasing temperature, and reaches about 3 K at low temperatures.