The magnetic structures of NdCu₂ determined by single crystal neutron diffraction

We investigated the magnetic structure of NdCu₂ by means of neutron diffraction as a function of temperature between 1.5 K and 8 K in zero external field. The diffraction data were obtained on two single crystals with different orientations using the triple-axis-spectrometer TAS6 at the DR-3 reactor at Risø. Two magnetic phases were observed between 1.5K and T_N=6.5K. From 1.5 K to 4.1 K the magnetic reflections can be described by the commensurate wave vector τ=(3/5 0 0) and its higher harmonics 3τ and 5τ. Below 2.5K the structure is completely squared-up. For 4.1 K≦T≦6.5 K the magnetic structure is incommensurate with the chemical lattice and can be described by the wave vector τ=(3/5 0 0) and its higher harmonies 3 τ and 5 τM. Below 2.5 K the structure is completely squared-up. For 4.1 K ≦T≦ 6.5 K the magnetic structure is incommensurate with the chemical lattice and can be described by the wave vector τ*=(0.62 0.044 0). In both phases the Nd-moments are oriented along the easy b-direction.