Atomic structural basis for magnetic field regulating nucleation behavior in monometallic Al and Zn melts

We investigated the atomic-scale structural evolution of liquid zinc (Zn) and aluminum (Al) under the influence of a 0.3/0.4 T static magnetic field using in situ high-energy X-ray diffraction. Our results reveal distinct responses to the magnetic field: the first coordination shell of liquid Zn expands, while that of Al contracts, indicating that the magnetic field differentially affects atomic aggregation in these metals, which further influences the solid-liquid interfacial energy (γ) during the subsequent nucleation process. Specifically, the magnetic field increases γ in Zn, hindering nucleation, while decreasing γ in Al, thereby promoting nucleation. This contrasting behavior arises from the distinct magnetic properties of the two metals and their corresponding responses to the magnetic field, consistent with the magnetic dipole theory. By elucidating the atomic-scale mechanisms through which magnetic fields influence nucleation, this study provides a foundation for tailoring solidification microstructures through the controlled application of magnetic fields.