Dark Field X-ray Microscopy Below Liquid-Helium Temperature: The Case of NaMnO2

TL;DR

This study demonstrates the application of dark field X-ray microscopy at liquid-helium temperatures to investigate phase transitions in NaMnO2, revealing local heterogeneities associated with its antiferromagnetic transition.

Contribution

It presents the first high-resolution DFXM experiment at cryogenic temperatures on NaMnO2, expanding the technique's applicability to low-temperature quantum materials.

Findings

Detected nanoscale triclinic domains below 45 K

Revealed local structural heterogeneities during phase transition

Established feasibility of low-temperature DFXM for quantum materials

Abstract

Dark field X-ray microscopy (DFXM) is an experimental technique employed to investigate material properties by probing their 'mesoscale,' or microscale structures, in a bulk-sensitive manner using hard X-rays at synchrotron radiation sources. However, challenges remain when it comes to applications of this technique to examine low-temperature phenomena in quantum materials, which exhibit complex phase transitions at cryogenic temperatures. One such material is NaMnO2, which hosts an antiferromagnetic transition at 45 K that is suspected to coincide with local structural transitions from its majority monoclinic phase to nanoscale triclinic domains. Direct observation of local heterogeneities and this effect at low temperatures in NaMnO2 is an important step in understanding this material, and serves as an ideal candidate study for expanding the DFXM experimental design space. This paper details a foundational high-resolution DFXM study, down to liquid-helium temperature and below, conducted to explore phase transitions in NaMnO2. The outlined experiment ushers in the evaluation of other functional materials at low temperatures using this technique.