Magnetic Order in single-crystalline YbPtSi

We report the first measurements on YbPtSi, which we synthesized as single crystals by means of flux growth from Indium. Single crystal x-ray diffraction measurements find that the YbPtSi crystal structure is the orthorhombic Co$_{2}$Si-type, with one crystallographic site for Yb. Magnetic susceptibility measurements find Curie-Weiss behavior above 100 K with a moment of 4.35 $\mu _{B}$, close to the 4.54 $\mu _{B}$ expected for trivalent Yb.~ Measurements of the heat capacity find a mean field-like magnetic ordering transition at T=4.65K. DC-susceptibility measurements show substantial single ion anisotropy, but also exhibit a peak at 4.65 K, indicating possible~antiferromagnetic ordering. The electrical resistivity is metallic, and the magnetic ordering is accompanied by a change in slope. The magnetic entropy amounts to only about 65 {\%} of Rln2 expected from an ordering Yb ground state doublet at the ordering temperature, suggesting a possible role for the Kondo effect. Our measurements indicate that YbPtSi is an unusual example of an Yb-based Kondo lattice system, ordering at an unusually high temperature.