Abstract
The evolution of the nuclear and magnetic structures of TlFe1:6Se2 was determined in the temperature
range of 5-450K using single crystal neutron di raction. The Fe layers in these materials
develop a corrugation in the magnetically ordered state. A canting away from the block checkerboard
magnetic structure is observed in the narrow temperature range between approximately 100 and
150 K. In this same temperature range, an increase in the corrugation of the Fe layers is observed.
At lower temperatures, the block checkerboard magnetic structure is recovered with a suppressed
magnetic moment and abrupt changes in the lattice parameters. Microstructure analysis at 300K
using atomic-resolution Z-contrast scanning transmission electron microscopy does not show the
clear phase separation observed in alkali-metal iron selenides. These ndings highlight the di erences
between the alkali-metal and thallium materials, and indicate competition between magnetic
ground states and a strong coupling of magnetism to the lattice in TlFe1:6Se2.
