THEORY OF MAGNETIC-STRUCTURES OF CSCUCL3 IN TRANSVERSE MAGNETIC-FIELD

At zero field CsCuCl3 is known to form a helical spin structure along the c-axis and the 120-degrees structure in the c-plane. This paper di scusses theoretically the effect of a magnetic field applied perpendic ular to the c-axis, which breaks the axial symmetry. First the classic al ground state is studied. The transverse magnetic field deforms the helical spin structure and causes a continuous phase transition from t he helical (i.e. incommensurate) spin structure to a commensurate stat e, as the field increases. Detailed studies are made of the helix pitc h and of the nature of the inconunensurate spin structure as functions of the field. The commensurate state has a nontrivial degeneracy, whi ch is lifted by quantum (and thermal) fluctuations. Therefore the 1/S expansion is applied to determine the spin structure of the commensura te state. From these studies possible spin structures are suggested fo r each region of field strength.