MAGNETIC TRANSITIONS IN LAYERED TRIANGULAR ANTIFERROMAGNETS

Magnetic states and phase transitions of the layered triangular antife rromagnets in an applied field are studied. It is shown that in compou nds like VBr2 and VCl2 quantum effects change the ground state structu re and cause successive phase transitions as the magnetic field increa ses. Coplanar structures of different spin configuration are realized far from the saturation field and a noncoplanar structure of umbrella- type configuration is realized near this field. The ground-state phase diagram is constructed, and a finite region of fields where the colli near phase is also possible is indicated.