The intermetallic compound Fe 2 AlTi (alternatively Fe 2 TiAl) is an important phase in the ternary Fe-Al-Ti phase diagram. Previous theoretical studies showed a large discrepancy of approximately an order of magnitude between the ab initio computed magnetic moments and the experimentally measured ones. To unravel the source of this discrepancy, we analyze how various mechanisms present in realistic materials such as residual strain effects or deviations from stoichiometry affect magnetism. Since in spin-unconstrained calculations the system always evolves to the spin configuration which represents a local or global minimum in the total energy surface, finite temperature spin effects are not well described. We therefore turn the investigation around and use constrained spin calculations, fixing the global magnetic moment. This approach provides direct insight into local and global energy minima (reflecting metastable and stable spin phases) as well as the curvature of the energy surface, which correlates with the magnetic entropy and thus the magnetic configuration space accessible at finite temperatures. Based on this approach, we show that deviations from stoichiometry have a huge impact on the local magnetic moment and can explain the experimentally observed low magnetic moments.

Central European Institute of Technology CEITEC MU Masaryk University Kamenice 5 CZ 625 00 Brno Czech Republic

Department of Chemistry Faculty of Science Masaryk University Kotlářská 2 CZ 611 37 Brno Czech Republic

Department of Condensed Matter Physics Faculty of Science Masaryk University Kotlářská 2 CZ 611 37 Brno Czech Republic

Department of Physical Metallurgy and Materials Testing Montanuniversität Leoben Franz Josef Strasse 18 A 8700 Leoben Austria

Institute of Physics of Materials Academy of Sciences of the Czech Republic Žižkova 22 CZ 616 62 Brno Czech Republic

Max Planck Institut für Eisenforschung GmbH Max Planck Str 1 D 40237 Düsseldorf Germany

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