Upper critical field of a ${\mathrm{Sm}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$ single crystal: Interaction between superconductivity and antiferromagnetic order in copper oxides

The temperature dependence of the anisotropic upper critical magnetic field, ${\mathrm{H}}_{\mathrm{c}2}$(T), has been determined resistively in antiferromagnetic ${\mathrm{Sm}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$ 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≊0.1 eV and the Ginzburg-Landau coherence lengths ${\xi }_{\mathrm{ab}}$=79 Å and ${\xi }_{\mathrm{c}}$=14.7 Å are obtained. In both ${\mathrm{Nd}}_{1.84}$ ${\mathrm{Ce}}_{0.16}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$ and ${\mathrm{Sm}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$, 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/${\mathit{T}}_{\mathit{c}}$ ${)}^{1.6}$.