  The Fe1+y Te1-x Sex compounds belong to the family of iron-based high
temperature superconductors, in which superconductivity often appears upon
doping antiferromagnetic parent compounds. Unlike other Fe-based
superconductors (in which the antiferromagnetic order is at the Fermi surface
nesting wavevector [1/2,1/2,1]), the Fe1+y Te1-x Sex parent compound Fe1+y Te
orders at a different wavevector, [1/2, 0, 1/2]. Furthermore, the ordering
wavevector depends on y, the occupation of interstitial sites with excess iron;
the origin of this behavior is controversial. Using inelastic neutron
scattering on Fe1.08 Te, we find incommensurate magnetic fluctuations above the
Neel temperature, even though the ordered state is bicollinear and commensurate
with gapped spin waves. This behavior can be understood in terms of a
competition between commensurate and incommensurate order, which we explain as
a lock-in transition caused by the magnetic anisotropy.
