Abstract
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 ∼ 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 (0.48, 0, 0.5), and correlation length of 12 ËšA along the a axis and 9 ËšA 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 longrange
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.
