Abstract
An unexplained discrepancy exists between the experimentally measured and theoretically calculated magnetic moments of Mn in \ensuremath{\alpha}-Fe. In this study, we use density functional theory to suggest that this discrepancy is likely due to the local strain environment of a Mn atom in the Fe structure. The ferromagnetic coupling, found by experiment, was shown to be metastable and could be stabilized by a 2% hydrostatic compressive strain. The effects of Mn concentration, vacancies, and interstitial defects on the magnetic moment of Mn are also discussed. It was found that the ground-state, antiferromagnetic (AFM) coupling of Mn to Fe requires long-range tensile relaxations of the neighboring atoms along $\ensuremath{\langle}111\ensuremath{\rangle}$ which is hindered in the presence of other Mn atoms. Vacancies and Fe interstitial defects stabilize the AFM coupling but are not expected to have a large effect on the average measured magnetic moment.
Highlights
Steels are ubiquitous in technological applications due to the abundance and low cost of Fe and its highly desirable mechanical and corrosion properties with alloying additions
It was found that the ground-state, antiferromagnetic (AFM) coupling of Mn to Fe requires long-range tensile relaxations of the neighboring atoms along 111 which is hindered in the presence of other Mn atoms
The state-of-the art theoretical description of Mn in Fe has a large impact on our understanding of phenomena such as solute clustering [1] and vacancy-solute clustering [2], which compromise the structural integrity of the steels during operation
Summary
Steels are ubiquitous in technological applications due to the abundance and low cost of Fe and its highly desirable mechanical and corrosion properties with alloying additions. The state-of-the art theoretical description of Mn in Fe has a large impact on our understanding of phenomena such as solute clustering [1] and vacancy-solute clustering [2], which compromise the structural integrity of the steels during operation The former occurs in the ferritic phase of duplex steels as a result of thermal aging (573–773 K for >1000 h) [3,4,5] and in low-alloy steels [6,7,8] resulting from long-term (>1 year) elevated temperature (∼550 K); the latter occurs due to neutron irradiation damage, which is of interest to life extension of nuclear fission reactors and for fast neutron damage of steels to be used in future fusion reactors. We use density functional theory (DFT) to study the effect of concentration, local environment, strain, and point defects on the magnetic moment and stability of Mn in α-Fe
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