Interstitial iron tuning of the spin fluctuations in the nonsuperconducting parent phase Fe1+xTe

Using neutron inelastic scattering, we investigate the low-energy spin fluctuations in Fe1+xTe as a function of both temperature and interstitial iron concentration. For Fe1.057(7)Te, the magnetic structure is defined by a commensurate wave vector of (12,0,12). The spin fluctuations are gapped with a sharp onset at 7 meV and are three dimensional in momentum transfer, becoming two dimensional at higher-energy transfers. On doping with interstitial iron, we find, in Fe1.141(5)Te, the ordering wave vector is located at the (0.38,0,12) position and the fluctuations are gapless with the intensity peaked at an energy transfer of 4 meV. These results show that the spin fluctuations in the Fe1+xTe system can be tuned not only through selenium doping, but also with interstitial iron. We also compare these results with superconducting concentrations and, in particular, the resonance mode in the Fe1+xTe1-ySey system. © 2011 American Physical Society.