Low-temperature studies of the magnetic and superconducting properties of theR2Ir3Si5(R=Y,La,Ce−Nd,Gd−Tm)system

Abstract

Polycrystalline samples of the ternary rare-earth silicide compounds R 2 Ir 3 Si 5 (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 (1.6-30 K) zero-field heat capacity measurements. All the compounds crystallize in the tetragonal U 2 Co 3 Si 5 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 Ce 2 Ir 3 Si 5 , 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 Ce 2 Rh 3 Si 5 . Pr 2 Ir 3 Si 5 also does not order down to 1.8 K. 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 Gd 2 Ir 3 Si 5 show three anomalies, one above and one below the main λ type antiferromagnetic transition peak at 11.8 K, while the data for Tb 2 Ir 3 Si 5 also suggest two transitions. Most of the compounds have transition temperatures which follow the de Gennes scaling. However, Nd 2 Ir 3 Si 5 and Tb 2 Ir 3 Si 5 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 30 K, and this could be a possible reason for the deviation of the ordering temperature T N from the de Gennes factor. From the temperature dependence of the magnetic entropy we conclude that Nd 2 Ir 3 Si 5 , Tb 2 Ir 3 Si 5 , Dy 2 Ir 3 Si 5 , and Ho 2 Ir 3 Si 5 are in a doublet ground state. The anomalies in the susceptibility and heat capacity near 2 K for La 2 Ir 3 Si 5 and 2.9 K for Y 2 Ir 3 Si 5 suggest that these compounds undergo a transition into the superconducting state at low temperatures. A reduced jump ΔC/γT C at T C 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 R 2 Fe 3 Si 5 , where it has been suggested that a fraction of the Fermi surface remains normal below T C .