Metallic Bond Induces Soft Phonon Mode and Anharmonicity in Heusler Alloy

The fruitful functional performances of metastable Heusler alloys originate from the martensitic transformation driven by the transverse acoustic soft phonon mode, regulated by anharmonicity. However, the origins of the soft mode and the anharmonicity in these alloys remain unclear. In this work, using ab-initio calculations combined with self-consistent phonon theory (SCPH) and compressed sensing techniques in machine learning, a link among chemical bonding, long-range interaction, soft mode, and anharmonicity is established using Ni₂MnGa as a model system. The long-range interaction rooted in metallic bonding between spin-down d-orbitals of Ni─Ni induces phonon softening and significant anharmonicity. This finding offers new insights into the role of metallic bonding and long-range interactions in martensitic transformation, providing a fresh perspective for the design and optimization of phase transition functional alloys.