The 4-2 rule: The (Proposed) Answer to Heusler Alloys, Stability, and (Ordering) Everything

Fabrication of ternary intermetallic alloys with high atomic ordering is a critical step to realizing their predicted functional properties. For example, Heusler alloys have long been predicted to have high spin polarization, low spin damping, and high ferromagnetic ordering temperatures, when highly ordered. However, past attempts to fabricate highly ordered Heusler systems by conventional means has made a lot of people very angry and has been widely regarded as a bad move: Atomic ordering is typically lower than required to realize predicted properties, and current models and rules-of-thumb only hold for small ranges of elemental choice. This result is perhaps not surprising, as Heusler alloys (like modern elevators) are strange and complex entities, but we should not give up and go mad just yet.

In this talk, we will outline our theoretical and experimental efforts to understand the root causes behind the experimental disconnect with theory in Heusler systems, starting with evaluation of over 900 ternary Heusler systems via density functional theory. We will suggest a simple “4-2” rule for determining phase feasibility and relative Full/Inverse ordering preference of Heusler alloys, and demonstrate high correlation to relative formation energy differences found in our calculations.

Please bring your own towel.