Ce2PtGe3: a new ordered orthorhombic superstructure in the AlB2 family with spin glass behavior

Abstract

A new compound Ce₂PtGe₃ was synthesized using arc-melting process. The compound crystallizes in an orthorhombic Cmce crystal structure with lattice parameters a = 8.5157(17) Å, b = 14.7496(29) Å and c = 4.2511(9) Å. The structure of Ce₂PtGe₃ can be derived from the structure of YAlGe, which is another superstructure derivative of the AlB₂ prototype crystallizing in the Cmcm space group. The crystal structure of Ce₂PtGe₃ is composed of infinite arrays of hexagonal [Pt₃Ge₃] units stacked along the b-axis and the Ce sites are sandwiched between these parallel hexagonal networks, which is closely related to the other known orthorhombic superstructures Ca₂AgSi₃ (SG: Fmmm) and Ba₂LiSi₃ (SG: Fddd) in the AlB₂ family. Both DC and AC susceptibility measurements reveal a spin glass state probably arising from non-magnetic atomic disorder (NMAD) from positional disorder from a part of Pt and Ge crystallographic sites. This was further supported by specific heat capacity measurements with a high value of γ = 125 mJ mol⁻¹ K⁻². The modified Curie–Weiss fitting yielded a residual magnetic moment (χ₀) 0.0011 emu mol⁻¹, and Curie paramagnetic temperature, θ_p = −21.5 K suggesting antiferromagnetic coupling and an effective magnetic moment of 3.09μ_B per Ce which indicates the presence of Ce³⁺. A thorough analysis of the temperature dependent resistivity data revealed that the compound might be a Kondo semiconductor at low temperature.