# Neutron diffraction study on phase transition and thermal expansion of SrFeAsF

## TL;DR

This study uses neutron diffraction to analyze phase transitions, magnetic ordering, and thermal expansion in SrFeAsF, revealing a tetragonal-orthorhombic transition at 180K, magnetic ordering at 133K, and insights into lattice dynamics.

## Contribution

It provides detailed neutron diffraction data on SrFeAsF's structural and magnetic phase transitions and thermal properties, which were previously not well characterized.

## Key findings

- Phase transition from tetragonal to orthorhombic at 180 K
- Paramagnetic to antiferromagnetic transition at 133 K
- FeAs layer expansion influences thermal expansion coefficient

## Abstract

The magnetic ordering and crystal structure of iron pnictide SrFeAsF was investigated by using neutron powder diffraction method. With decreasing temperature, the tetragonal to orthorhombic phase transition is found at 180 K, while the paramagnetic to antiferromagnetic phase transition set in at 133 K. Similar to the parent compound of other iron pnictide system, the striped Fe magnetism is confirmed in antiferromagnetic phase and the Fe moment of 0.58(6) uB aligned along long a axis. The thermal expansion of orthorhombic phase of SrFeAsF is also investigated. Based on the Grueneisen approximation and Debye approximation for internal energy, the volume of SrFeAsF can be well fitted with Debye temperature of 347(5) K. The experimental atomic displacement parameters for different crystallographic sites in SrFeAsF are analyzed with Debye model. The results suggested that the expansion of FeAs layers plays an important role in determining the thermal expansion coefficient.