NEUTRON-DIFFRACTION OF CSCUCL3 IN HIGH FIELDS

Neutron diffraction measurements of triangular lattice CsCuCl3 have be en performed in a pulsed high magnetic field up to 14 T. For an applie d field parallel to the c-axis and below B(c) = 10 T at 7 K, Bragg ref lection is observed at (1/3 1/3 0.085) showing a long period helical s pin alignment along the c-axis and a triangular umbrella-like structur e in the c-plane. The intensity of this reflection drastically changes at B(c) and a new reflection at (1/3 1/3 0) appears. These results we ll explain a new type of magnetic phase transition which cannot be und erstood by the classical theory. When B is perpendicular to the c-axis more complicated results are observed.