Observation of noncollinear magnetic structure for the Cu spins inNd2CuO4-type systems

Field-dependent neutron-diffraction measurements have been taken on ${\mathrm{Nd}}_2$ ${\mathrm{CuO}}_4$ and ${\mathrm{Sm}}_2$ ${\mathrm{CuO}}_4$ in order to distinguish between the proposed collinear and noncollinear spin structures for the Cu ions. For magnetic fields applied along the (110) direction, both systems exhibit Bragg intensities that are continuous and reversible with H. For ${\mathrm{Nd}}_2$ ${\mathrm{CuO}}_4$ we have also taken data for fields applied within an angle α of the (100) direction, and we have found that the intensities of the magnetic reflections increase or decrease depending on the sign of α. Both of these observations are only consistent with the noncollinear spin model.