ON THE FIELD-DEPENDENT MAGNETIC-STRUCTURES OF CSCUC1(3)

Neutron diffraction results on single crystals of CsCuCl3 in high magn etic fields are reported. The fields were applied parallel (up to abou t 6.5 T) and perpendicular (up to 8.5 T) to the c axis of the hexagona l crystal. For the parallel field a spin-flop-like change in the magne tic structure at fields above 5.6 T was observed close below the Neel temperature. The magnetic phase diagram has been determined in the tem perature range between 9.6 K and T-N = 10.675 K. In the perpendicular field the magnetic satellite reflections, originating from the helical magnetic spin structure of the Cu ions, shift their positions in risi ng field, indicating a stretching out of the helices. The results are interpreted in the light of recent theoretical predictions about the t ransitions being triggered by quantum or thermal fluctuations. In addi tion to determining the spin structures, we find that the critical exp onent beta is close to 0.25 in the low-field phase and probably close to 0.125 in the high-field phase.