ScholarWorks@숙명여자대학교

초록

This paper presents an analytical model for the maximum energy product ((BH)max) in core-shell structured magnetic exchange-coupled nanomagnets. The model was validated by comparing its results to the (BH)max from core-shell magnets reported in the literature. This approach can serve as a universal model for designing core-shell magnets that achieve the desired (BH)max. The (BH)max was determined under two distinct nucleation field (HN) conditions: HN ≤ Mr/2 and HN ≥ Mr/2, where Mr is the remanent magnetization. Additionally, two different values of magnetic hysteresis loop squareness (SQ = Mr/MS) were used: 1.0 and 0.7. The soft magnetic shell’s remanent magnetic flux density (Br) ranged from 0.7 to 2.2 T, while the core diameter (Dh) varied between 50 and 250 nm in this (BH)max model. The LTP (low-temperature phase) MnBi-core/soft-shell nanomagnet can achieve a (BH)max of 40 MGOe at a Br of 1.6 T, with a shell thickness (δS) of 40 nm, a Dh of 250 nm, and a volume fraction of the hard-core (fh) of 0.43. The (BH)max of the hexaferrite (SrFe12O19)/soft-shell (1.9 T) nanomagnet can be improved from 5.8 (single hexaferrite phase) to 20 MGOe. This approach achieves the desired (BH)max of the rare-earth-free permanent magnet, thereby tackling issues related to rare-earth mineral security and unstable supply chains.

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