THE MAGNETIC-STRUCTURES OF NDCU2 IN ZERO-FIELD

The magnetic structure of NdCu2 has been investigated by means of neutron diffraction as a function of temperature between 1.4 K and 8 K in zero external field. The diffraction patterns were obtained on the multidetector DN5 at the SILOE reactor of CENG. Two magnetic phases were observed between 1.4 K and T(N) = 6.5 K. In both phases the magnetic structure can be described by an oscillating component of the Nd moments, which are oriented along the b-direction. In the high-temperature phase between 5.2 K and T(N) a sinusoidal oscillating component with wavevector tau* = (0.62, 0.042, 0) is obtained. Accordingly, the magnetic structure is incommensurate with the lattice. Below 4 K the structure becomes commensurate with the lattice and the wavevector is given by tau = (0.6, 0, 0). This means that in the low-temperature phase the structure is exactly a transversely oscillating component. Additionally a progressive squaring up from the appearance of the third harmonic 3tau in the range from 4.0 K down to 1.4 K is observed. At 1.4 K the amplitudes of the fundamental and the third harmonic oscillation are 2.32mu(B) and 0.9mu(B), respectively. The ratio of these two values agrees with that expected for complete squaring up. Around 4.4 K the spectra seem to be determined by a superposition of the high- and low-temperature phases.