NEUTRON-DIFFRACTION STUDY OF THE MAGNETIC PHASE-DIAGRAM OF RBMNBR3 - OBSERVATION OF THE CRITICAL LINE OF FIELD-INDUCED PHASE-TRANSITION

Neutron diffraction measurements of single-crystal RbMnBr3 have been p erformed under magnetic fields applied parallel to the a-axis of the prototype lattice, where the structural phase transitions are not take n into account. The critical line of a field-induced phase transition, at which the modulation wave number of the spin structure changes, ha s been obtained in the magnetic phase diagram for 4.2 < T < 11 K and 0 < H < 5.0 T, in addition to the in-c-plane spin-flop phase transition .