Triangular antiferromagnets with a layered structure in a uniform field

We study the magnetic states and phase transitions in layered triangular antiferromagnets and show that in compounds of the VBr2 (or VCl2) type the quantum effects alter the structure of the ground state and initiate a series of transitions as the magnetic field strength is increased. We establish that planar structures with different spin configurations are realized when the magnetic field strength is far from the saturation value, while a nonplanar structure of the umbrella type is realized in fields close to the saturation value. Finally, we build the phase diagram of the ground state and indicate a finite range of field strengths where a collinear phase is possible, too. (C) 1997 American Institute of Physics.