Atomic-Scale Transition Zones Determined Coercivity in Samarium-Cobalt Based Permanent Magnets

SmCo-based permanent magnets with nanocellular structure exhibit significant advantage for high-temperature applications. Due to the lack of experimental intrinsic magnetic parameters and unclear nanocellular interface, a fully understanding on coercivity mechanism is still limited. Here the intrinsic magnetic properties of designed two single-phase alloys representing nanocellular structure at various temperatures are acquired. Using 3D atom probe and high-angle annular dark-field scanning transmission electron microscopy, the existence of the nanoscale transition zones located at nanocellular interface is revealed. Moreover, the transition zones exhibiting high magnetocrystalline anisotropy is found to contribute dominantly to the coercivity. The calculated coercivity via micromagnetic simulation considering transition zones agrees well with the tested coercivity at various temperatures. This knowledge deepens the fundamental understanding on coercivity mechanism.