Real space imaging of tuneable magnetic order in Fe_1+xTe with x>0.12

Magnetism is thought to play an important role in the development of the superconductivity in the Iron chalcogenide superconductors. In the parent material, FeTe, the magnetic phase diagram is very complex with unusual magnetic states developing as a function of excess Iron doping [1].
We have conducted a spin-polarized scanning tunnelling microscopy study on samples of FeTe with different levels of excess Iron concentrations by in-situ prepared magnetic tips [2]. Using a ferromagnetic tip in a cryogenic STM in a vector magnetic field [3,4], we have been able to map out the magnetic order at the surface on an atomic scale in all three spatial directions. By collecting Fe atoms from the surface with the STM tip the excess Fe concentration of the surface can be tuned locally. For samples of Fe_1+xTe with x>0.12 our results reveal a magnetic transition from a single-q to a multi-q order as a function of local excess iron concentration [4]. I will discuss these results and compare them with the neutron scattering measurements.
[1] – E.Rodriguez et al., Physical Review B 84 064403 (2011)
[2] – M.Enayat et al., Science 345, 653-656 (2014)
[3] – C.Trainer et. al., Rev. Sci. Instr. 88, 093705 (2017)
[4] – C.Trainer et. al. arXiv:1802.05978 (2018)