  Using mean-field theory, exact diagonalizations and SU(3) flavour theory, we
have precisely mapped out the phase diagram of the S=1 bilinear-biquadratic
Heisenberg model on the triangular lattice in a magnetic field, with emphasis
on the quadrupolar phases and their excitations. In particular, we show that
ferroquadrupolar order can coexist with short-range helical magnetic order, and
that the antiferroquadrupolar phase is characterized by a remarkable 2/3
magnetization plateau, in which one site per triangle retains quadrupolar order
while the other two are polarized along the field. Implications for actual S=1
magnets are discussed.
