Electronic structure, magnetic structure, and metal-atom site preferences in CrMnAs

Thumbnail Image
Date
2013-01-01
Authors
Lutz, Laura
Major Professor
Advisor
Gordon J. Miller
Scott Beckman
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Altmetrics
Authors
Research Projects
Organizational Units
Organizational Unit
Materials Science and Engineering

The Department of Materials Science and Engineering teaches the composition, microstructure, and processing of materials as well as their properties, uses, and performance. These fields of research utilize technologies in metals, ceramics, polymers, composites, and electronic materials.

History
The Department of Materials Science and Engineering was formed in 1975 from the merger of the Department of Ceramics Engineering and the Department of Metallurgical Engineering.

Dates of Existence
1975-present

Related Units

Journal Issue
Is Version Of
Versions
Series
Abstract

Density functional theory was used to examine stoichiometric CrMnAs, one of a class of 3d-metal arsenides that exhibit cooperative magnetic ordering. CrMnAs is a tetragonal structure with two inequivalent metal sites: M(I), which is tetrahedral coordinate, and M(II), which is square pyramidal coordinate. CrMnAs thus presents a “coloring problem,” the question of how the two types of metal atoms are distributed between the two types of metal sites. Previous diffraction studies have determined that CrMnAs is antiferromagnetic with the M(I) site primarily occupied by Cr.

TB-LMTO-ASA local density approximation (LDA) calculations showed indications of instability in the nonmagnetic structure, which could be resolved either by structural distortion or by spin polarization. LDA crystal orbital Hamilton population (COHP) curves were used to predict the nature of particular direct-exchange interactions upon spin polarization. Spin-polarized total energy calculations were performed using VASP with the generalized gradient approximation (GGA).

The lowest-energy structure had Mn at the M(I) site and a different antiferromagnetic ordering than previously observed. The structure with the second-lowest calculated total energy also had Mn at M(I). Next lowest were four structures with Cr at M(I), including the experimentally observed structure. Those four had calculated total energies ranging from 154.2 to 167.8 meV/f.u. higher than the lowest-energy case. The number of possible structures with small energy differences suggests that the observed magnetic ordering and coloring may be due to entropy rather than reflecting a true electronic ground state.

Comments
Description
Keywords
Citation
Source
Copyright
Tue Jan 01 00:00:00 UTC 2013