Upper critical field of a Sm1.85Ce0.15CuO4-y single crystal: Interaction between superconductivity and antiferromagnetic order in copper oxides.

Abstract

The temperature dependence of the anisotropic upper critical magnetic field, ${\mathrm{H}}_{\mathrm{c}2}$(T), has been determined resistively in antiferromagnetic ${\mathrm{Sm}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{y}}$ single crystals. We observe the first evidence in high-${\mathrm{T}}_{\mathrm{c}}$ copper oxides for the interaction between superconductivity and antiferromagnetic ordering of rare-earth ions; estimates of the exchange coupling J\ensuremath{\approxeq}0.1 eV and the Ginzburg-Landau coherence lengths ${\ensuremath{\xi}}_{\mathrm{ab}}$=79 A\r{} and ${\ensuremath{\xi}}_{\mathrm{c}}$=14.7 A\r{} are obtained. In both ${\mathrm{Nd}}_{1.84}$${\mathrm{Ce}}_{0.16}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{y}}$ and ${\mathrm{Sm}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{y}}$, the ${\mathrm{H}}_{\mathrm{c}2}$ data above ${\mathrm{T}}_{\mathrm{N}}$ can be described by ${\mathit{H}}_{\mathit{c}2}$(T)/${\mathit{H}}_{\mathit{c}2}^{+}$(0)=(1-T/${\mathit{T}}_{\mathit{c}}$${)}^{1.6}$.