SPIRAL PHASES IN EASY-PLANE J(1)-J(2)-J(3) TRIANGULAR ANTIFERROMAGNETS

We present the phase diagram of the S = 1/2 Heisenberg antiferromagnet on triangular lattices with second and third nearest-neighbor couplin gs (J(1)-J(2)-J(3) model). In addition to the classical three-sublatti ce and collinear states, the spin-wave analysis predicts three novel i ncommensurate spiral phases. For sufficiently small site spins S there exist regions on the phase diagram where the classical spiral states are completely destroyed by quantum fluctuations.