Type-II superconductivity in a dilute magnetic system: La1-xTmxRu3Si2.

Abstract

Superconducting and magnetic properties of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Tm}}_{\mathit{x}}$${\mathrm{Ru}}_{3}$${\mathrm{Si}}_{2}$ (x=0, 0.08, and 0.16) have been investigated through measurements of both electric and magnetic properties. Tm is in a trivalent state and carries a magnetic moment \ensuremath{\approxeq}8${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. We find that the magnetic measurements are not suited to the determination of the critical line ${\mathit{H}}_{\mathit{c}}$(T) for the onset of type-II superconductivity in materials where one has at the same time superconducting diamagnetic shielding and paramagnetic contribution due to the localized spins. On the other hand, transport experiments are much less ambiguous, and allow us to determine accurately the critical temperature in a given applied magnetic field. In particular, they allow us to suggest a more appropriate interpretation of the maximum in the magnetic-susceptibility curve already observed in materials of the same family: this maximum results from a competition between the incomplete diamagnetic shielding and the paramagnetic contribution from the magnetic ions in the mixed phase, rather than from a spin-glass freezing of the paramagnetic ions. In zero field, the rate of depression of the critical temperature upon substituting nonmagnetic La ions by magnetic Tm ions is dT/dx=-8\ifmmode\pm\else\textpm\fi{}1 K/at. % Tm.