Superconductivity and magnetism in the La2-xNdxRh3Si5 system.

Abstract

It is now well known that the compounds that belong to the ${\mathit{R}}_{2}$${\mathrm{Fe}}_{2}$${\mathrm{Si}}_{5}$ series exhibit unusual superconducting and magnetic properties. Although a reasonable number of studies have been made on this series, similar efforts on another series, namely, ${\mathit{R}}_{2}$${\mathrm{Rh}}_{3}$${\mathrm{Si}}_{5}$, whose structure is closely related to ${\mathit{R}}_{2}$${\mathrm{Fe}}_{3}$${\mathrm{Si}}_{5}$ have not been made. In this paper, we have established the bulk superconductivity in ${\mathrm{La}}_{2}$${\mathrm{Rh}}_{3}$${\mathrm{Si}}_{5}$ below 4.4 K and bulk antiferromagnetism in ${\mathrm{Nd}}_{2}$${\mathrm{Rh}}_{3}$${\mathrm{Si}}_{5}$ below 2.7 K, from resistivity, susceptibility, and heat-capacity studies. The superconducting transition temperature of (${\mathit{T}}_{\mathit{c}}$) ${\mathrm{La}}_{2}$${\mathrm{Rh}}_{3}$${\mathrm{Si}}_{5}$ decreases with the Nd substitution for La and we have analyzed this ${\mathit{T}}_{\mathit{c}}$ dependence using Abrikosov and Gor'kov theory with crystal-field contributions. The estimated value of the interaction between the conduction electrons and the rare-earth spin (${\mathit{J}}_{\mathit{s}\mathit{f}}$) is 37 meV which is adequate to suppress the coexistence of superconductivity and antiferromagnetism in ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Nd}}_{\mathit{x}}$${\mathrm{Rh}}_{3}$${\mathrm{Si}}_{5}$ alloys above 0.6 K. Finally, we have also analyzed the temperature dependence of the upper critical field of Nd-doped ${\mathrm{La}}_{2}$${\mathrm{Rh}}_{3}$${\mathrm{Si}}_{5}$ alloys using a theory which incorporates spin-orbit coupling with an additional pair breaking parameter.