Nature of the Antiferromagnetic Order in GdCu${}_2$

A magnetic order in orthorhombic GdCu${}_2$ was investigated via a single crystal neutron diffraction with thermal neutron. Magnetic peaks were observed at incommensurate positions described by the ordering vector $q$=($\delta$,~1,~0) with $\delta$=0.678 at 4.6~K. This ordering vector is close to the commensurate one with $q_{\mathrm{c}}$=(2/3,~1,~0) reported earlier, but clearly deviates. The incommensurate nature of the magnetic order in GdCu${}_2$ is further corroborated by the peak shift with temperature below $T_{\mathrm{N}}$.