Magnetism and superconductivity in the Heusler alloy Pd 2 YbPb

• Published in: Journal of applied physics 2012-02, Vol.111 (7), p.07E111-07E111-3
• Main Author: Öner, Y.
• Format: Article
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.3671780

We report the temperature dependence (1.8-300 K) of the heat capacity (C p ) and electrical resistivity (ρ) for the Heusler alloy Pd 2 YbPb and its isomorphous nonmagnetic counterpart, Pd 2 YPb. Both compounds appear to be the same MnCu 2 Al structure with space group Fm 3 ¯ m . From the resistivity data, the superconducting transition for Pd 2 YbPb and Pd 2 YPb are observed at T=2.85 K and T=4.75 K, respectively. At low temperatures, the Cp/T versus T data exhibits a small jump at around 4 K for Pd 2 YPb, while, for Pd 2 YbPb, this superconducting transition is hidden by an upturn feature observed below T=3 K, presumably due to nuclear spin polarization. From low temperature analysis of the Cp/T data, the electronic contribution to C p and Debye temperature were determined to be γ=4.5 mJ/mole-K and Θ D =140 K for Pd 2 YbPb and γ=1.6 mJ/mole-K and Θ D =173 K for Pd 2 YPb. The magnetic contribution of the Yb +3 ions to the heat capacity and resistivity were calculated by subtracting the Pd 2 YPb data from that for Pd 2 YbPb. The scheme of the energy levels created by the crystal electric field (CEF) splitting for cubic symmetry was determined from the Schottky contribution to C p . In addition, the effect of CEF on the resistivity has been investigated. Both analyses lead us to suggest that the ground state of Yb ions is a quartet Γ 8 . The first excited level between the ground state Γ 8 and a Γ 7 doublet, Δ 1 =125 K, and the second energy splitting between Γ 8 and Γ 6 , Δ 2 =268 K, were deduced from the heat capacity data, while values of Δ 1 =155 K and Δ 2 =355 K were obtained from resistivity data. Furthermore, at higher temperatures, we observed that C p for Pd 2 YbPb exceeds the Dulong-Petit limit, leading us to include a small anharmonic correction in the fitting analysis.