Magnetic ordering of Sm inSm2CuO4

Long-range antiferromagnetic order of the Sm ions in ${\mathrm{Sm}}_2$ ${\mathrm{CuO}}_4$ is observed via neutron diffraction at ${\mathit{T}}_{\mathit{N}}$=5.95 K. The magnetic structure consists of ferromagnetic sheets within the a-b planes, with the spins in alternate sheets aligned antiparallel. This spin structure and spin direction are completely different from those observed in any other copper-oxide superconductor system. The temperature dependence of the upper critical field ${\mathit{H}}_{\mathit{c}2}$ for the superconductor ${\mathrm{Sm}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_4$ (${\mathit{T}}_{\mathit{c}}$=23.5 K) shows a sudden increase in ${\mathit{H}}_{\mathit{c}2}$ at T/${\mathit{T}}_{\mathit{c}}$∼0.7, but this anomaly cannot be attributed to the Sm magnetic ordering. No anomaly in ${\mathit{H}}_{\mathit{c}2}$ is observed at the ${\mathit{T}}_{\mathit{N}}$ for Sm.