Atomic structure evolution of magnetic HoErCo alloy metallic glass microwires at cryogenic temperatures

The thermal strain in metallic glass (MG) can induce defect activation and alter the magnetocaloric properties, making it crucial to understand the atomic structure changes at cryogenic temperatures. This study investigated the evolution of the atomic structure and volume variation of HoErCo MG microwires as the temperature drops to the cryogenic level using in-situ high-energy synchrotron X-ray diffraction. As the temperature decreases, atomic vibrations diminish, and the disorder within the MG decreases due to cooling contraction, resulting in a reduction in average atomic volume. Through analysis of partial coordination numbers, the study revealed the formation of various solute-centered clusters during cooling. Specifically, larger rare earth (RE) elements tend to migrate toward the center of the clusters, while cobalt (Co) atoms move outward. In alloy microwires, RE atoms are more likely to aggregate with Co atoms, forming Co-RE clusters with Co at the center. This research provides a strategy for investigating the deformation and physical properties of amorphous alloys at cryogenic temperatures, potentially enabling accurate prediction of MG materials’ behavior under such conditions.