Lattice and magnetic instabilities in CaFe2As2: A single crystal neutron diffraction study

TL;DR

This study uses neutron diffraction to investigate the structural and magnetic phase transitions in CaFe2As2, revealing a coupled transition with detailed magnetic ordering and hysteresis behavior.

Contribution

It provides the first detailed neutron diffraction analysis showing the coupling between structural and magnetic transitions in CaFe2As2.

Findings

Structural transition at ~172.5K with hysteresis of 1K.

Concurrent magnetic ordering with a saturated moment of 0.80(5)μB/Fe.

Magnetic ordering temperature shifts with structural transition, indicating strong coupling.

Abstract

Neutron diffraction measurements of a high quality single crystal of CaFe2As2 are reported. A sharp transition was observed between the high temperature tetragonal and low temperature orthorhombic structures at TS = 172.5K (on cooling) and 173.5K (on warming). Coincident with the structural transition we observe a rapid, but continuous, ordering of the Fe moments, in a commensurate antiferromagnetic structure is observed, with a saturated moment of 0.80(5)muB/Fe directed along the orthorhombic a-axis. The hysteresis of the structural transition is 1K between cooling and warming and is consistent with previous thermodynamic, transport and single crystal x-ray studies. The temperature onset of magnetic ordering shifts rigidly with the structural transition providing the clearest evidence to date of the coupling between the structural and magnetic transitions in this material and the broader class of iron arsenides.