Magnetic phases in the J1−J2 Heisenberg antiferromagnet on the triangular lattice

We use series expansion methods to investigate the phase diagram of a spin-1/2 Heisenberg antiferromagnet on the triangular lattice with first- and second-neighbor interactions. We find regions of ${120}^{\ensuremath{\circ}}$ and collinear ``stripe'' order, separated by an intermediate nonmagnetic phase, in agreement with results obtained previously using other methods. Magnon excitation spectra in the ordered phases are also obtained, and discussed.