Abstract
The intermetallic compound FeAlTi (alternatively FeTiAl) 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.
Highlights
The Fe-Al-Ti ternary system is the basis for materials with a wide range of technologically interesting properties
We studied in detail how deviations from perfect crystal affect the local moment
In order to identify the reason why the density functional theory (DFT) computed ground state of Fe2 AlTi shows a much higher magnetic moment than is observed experimentally, we systematically searched for additional minima on the total energy landscape
Summary
The Fe-Al-Ti ternary system is the basis for materials with a wide range of technologically interesting properties. For example, medical applications [1,2], their ability to form oxygen-containing inclusions strenthening steels [3], their potential for high-temperature applications [4,5,6,7,8,9], and more [10,11,12,13,14,15,16]. A subset of these high-temperature materials are two-phase Fe-Al-Ti superalloys (e.g., [18,19,20,21]). Containing an off-stoichiometric Fe2 AlTi intermetallic compound. Stoichiometric Fe2 AlTi crystallizes in the Heusler L21 -structure. It was included in an extensive theoretical study by Gilleßen and Dronskowski in which they calculated properties of 810 different
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