  We study the effects of Cu substitution in Fe1.1Te, the non-superconducting
parent compound of the iron-based superconductor, Fe1+yTe1-xSex, utilizing
neutron scattering techniques. It is found that the structural and magnetic
transitions, which occur at \sim 60 K without Cu, are monotonically depressed
with increasing Cu content. By 10% Cu for Fe, the structural transition is
hardly detectable, and the system becomes a spin glass below 22 K, with a
slightly incommensurate ordering wave vector of (0.5-d, 0, 0.5) with d being
the incommensurability of 0.02, and correlation length of 12 angstrom along the
a axis and 9 angstrom along the c axis. With 4% Cu, both transition
temperatures are at 41 K, though short-range incommensurate order at (0.42, 0,
0.5) is present at 60 K. With further cooling, the incommensurability decreases
linearly with temperature down to 37 K, below which there is a first order
transition to a long-range almost-commensurate antiferromagnetic structure. A
spin anisotropy gap of 4.5 meV is also observed in this compound. Our results
show that the weakly magnetic Cu has large effects on the magnetic
correlations; it is suggested that this is caused by the frustration of the
exchange interactions between the coupled Fe spins.
