Low-temperature studies of the magnetic and superconducting properties of the R2Ir3Si5 (R=Y,La,Ce−Nd,Gd−Tm) system

Abstract

Polycrystalline samples of the ternary rare-earth silicide compounds R2Ir3Si5 (R=Y,La,Ce−Nd,Gd−Tm) have been prepared and characterized using room temperature powder x-ray, magnetic susceptibility, electrical resistivity, and low-temperature (1.6–30K) zero-field heat capacity measurements. All the compounds crystallize in the tetragonal U2Co3Si5 type structure (space group Ibam). The effective moments estimated from Curie-Weiss fits to the high-temperature inverse susceptibility data suggest that Ir may carry an induced moment in these compounds. The systematics of the lattice parameters across the series suggest that Ce is trivalent in Ce2Ir3Si5, whereas the magnetic, transport, and heat capacity measurements reveal a nonmagnetic behavior for this compound, suggesting that this is a strongly hybridized compound similar to Ce2Rh3Si5. Pr2Ir3Si5 also does not order down to 1.8K. Large and prominent peaks at low temperatures in the susceptibility and heat capacity of the other magnetic rare-earth-containing compounds indicate bulk magnetic ordering of trivalent rare-earth moments in these compounds. The heat capacity data for Gd2Ir3Si5 show three anomalies, one above and one below the main λ type antiferromagnetic transition peak at 11.8K, while the data for Tb2Ir3Si5 also suggest two transitions. Most of the compounds have transition temperatures which follow the de Gennes scaling. However, Nd2Ir3Si5 and Tb2Ir3Si5 have anomalously large transition temperatures compared to that expected by the de Gennes scaling. Large crystalline electric field effects are indicated by the reduced value of the magnetic entropy at 30K, and this could be a possible reason for the deviation of the ordering temperature TN from the de Gennes factor. From the temperature dependence of the magnetic entropy we conclude that Nd2Ir3Si5, Tb2Ir3Si5, Dy2Ir3Si5, and Ho2Ir3Si5 are in a doublet ground state. The anomalies in the susceptibility and heat capacity near 2K for La2Ir3Si5 and 2.9K for Y2Ir3Si5 suggest that these compounds undergo a transition into the superconducting state at low temperatures. A reduced jump ΔC∕γTC at TC and a large linear term in the temperature dependence of the heat capacity in the superconducting state are observed, and we compare this with similar behavior seen in the nonmagnetic superconducting members of the structurally related series R2Fe3Si5, where it has been suggested that a fraction of the Fermi surface remains normal below TC.

Source-reported materials — not catalogue approval

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