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Local Symmetry Deviation from the Average Structure of MnAs Revealed by Pair Distribution Function
Dipankar Saha1, Wojciech A Sławiński2, Susmit Kumar1
1Center for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway.
Inorganic Chemistry
|August 8, 2024
Summary
Investigating manganese arsenide (MnAs) reveals that local structural distortions hinder improvements in its magnetocaloric properties for magnetic refrigeration. Understanding these distortions is key to developing better magnetic cooling materials.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Solid State Chemistry
Background:
- Manganese arsenide (MnAs) exhibits promising magnetocaloric properties for magnetic refrigeration applications.
- Despite research efforts, enhancing MnAs's magnetic refrigeration performance through substitution has proven challenging.
- The inherent structure of MnAs may limit performance improvements in substituted forms.
Purpose of the Study:
- To investigate the local and average crystal structure of MnAs.
- To understand the relationship between local structural distortions and magnetocaloric performance.
- To identify reasons for the limited success in improving MnAs-based magnetic refrigeration.
Main Methods:
- Pair distribution function (PDF) modeling using both small and big box approaches for local structure analysis.
- Powder X-ray diffraction (PXRD) for determining the average crystal structure.
- X-ray absorption spectroscopy (XAS) combined with total scattering X-ray diffraction (TSXRD) for comprehensive structural insights.
Main Results:
- An inherent local orthorhombic distortion within the hexagonal MnAs structure was identified.
- Structural modifications to the hexagonal phase result in an orthorhombic structure.
- This induced orthorhombic structure is associated with weaker magnetocaloric performance.
Conclusions:
- Local structural distortions significantly impact the magnetocaloric properties of MnAs.
- The inherent orthorhombic distortion prevents performance gains in substituted MnAs.
- Studying local distortions is crucial for optimizing magnetic materials for refrigeration.
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