Kondo-like behavior in magnetic and thermal properties of single-crystal Tm5Si2Ge2

A stoichiometric Tm5Si2.0 +/- 0.1Ge2.0 +/- 0.1 single crystal was grown using the Bridgeman method and was examined by x-ray diffraction, energy dispersive spectroscopy, magnetization, ac and dc magnetic susceptibilities, specific heat, electrical resistivity, and x-ray photoemission spectroscopy experiments. Tm5Si2.0 +/- 0.1Ge2.0 +/- 0.1 was found to crystallize with an orthorhombic Sm5Ge4-type structure. The mean valence of Tm ions in Tm5Si2.0 +/- 0.1Ge2.0 +/- 0.1 was almost trivalent. The 4f states were split by the crystalline electric field. The ground state exhibited long-range antiferromagnetic order along the b axis below 8.01 K with the ferromagnetically coupled magnetic moments in the ac plane, whereas the exited states showed a reduced magnetic moment and magnetic entropy and -log T behaviors.