Magnetic and physical properties of new hexagonal compounds PrPt_4X (X = Ag, Au) release_yvrqqh6qpjhyhbrv6x7xtsjule

Abstract

We have synthesized PrPt_4Ag and PrPt_4Au compounds for the first time and report their crystal structure, as well as magnetic and physical properties in the temperature range of 1.9 K to 300 K. Both compounds are derived from the substitution of Pt with Ag and Au, respectively in the parent compound PrPt_5 which crystallizes in the hexagonal CaCu_5-type structure. Here we observed the preservation of the hexagonal CaCu_5-type structure under such substitutions, which is in contrast to the observations in PrCu_4Ag and PrCu_4Au adopting the cubic MgCu_4Sn-type structure upon substitution on parent hexagonal PrCu_5. The temperature dependences of specific heat C_p(T), and electrical resistivity ρ(T) of PrPt_4Ag show an anomaly at 7.6 K. This is absent in the magnetic susceptibility χ(T), thus suggesting a possible multipolar ordering of the Pr^3+ moment. PrPt_4Au on the other hand does not show any anomaly but an upturn in C_p(T)/T below about 10 K and attains 1.23 J/(mol K^2) at 1.9 K. In addition, ρ(T) ∼ T for nearly a decade in temperature. These observations for PrPt_4Au are the hallmark of a non-Fermi liquid (nFL) behavior and is characteristic of a system near a quantum critical point. The analyses of the low-temperature C_p(T) for PrPt_4Ag and PrPt_4Au give values of the Sommerfeld coefficient, γ = 728.5 mJ/(mol K^2) and 509.1 mJ/(mol K^2), respectively, indicating a significant enhancement of the quasiparticle mass in the two compounds.
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