Evolution of the nuclear and magnetic structures of TlFe1.6Se2 with temperature

TL;DR

This study investigates how the nuclear and magnetic structures of TlFe$_{1.6}$Se$_2$ evolve with temperature, revealing changes in magnetic ordering, layer corrugation, and lattice parameters, with implications for magnetic-lattice coupling.

Contribution

It provides detailed temperature-dependent structural and magnetic data for TlFe$_{1.6}$Se$_2$, highlighting differences from alkali-metal counterparts and showing strong magneto-lattice interactions.

Findings

Magnetic structure transitions around 100-150 K.

Layer corrugation increases with temperature.

Magnetic and structural properties are strongly coupled.

Abstract

The evolution of the nuclear and magnetic structures of TlFe$_{1.6}$Se$_2$ was determined in the temperature range of 5-450\,K using single crystal neutron diffraction. 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 300\,K using atomic-resolution Z-contrast scanning transmission electron microscopy reveals regions with ordered and disordered Fe vacancies, and the iron content is found to be uniform across the crystal. These findings highlight the differences between the alkali-metal and thallium materials, and indicate competition between magnetic ground states and a strong coupling of magnetism to the lattice in TlFe$_{1.6}$Se$_2$.