A binary alloy Mn0.5+xBi0.5-x, x ≤ 0.05, is a promising rare-earth-free magnetic material of high-energy-density (a critical module for electric motors and power electronics) with its economic value and profound magnetic properties for multiple uses at room temperature. In this article, we report how a free Bi, when precipitated over Mn0.5+xBi0.5-x(x ≤ 0.05) of small crystallites, diffuses back into a stable Mn0.5+xBi0.5-x, x → 0, via a peritectic reaction, which facilitates grow it preferentially in multiple facets of small core-shell crystallites, with duly tailored magnetic properties. It travels slowly in anisotropic channels of vacancies on annealing a reactive nanopowder at a critical 573 K temperature in Ar gas. An initial crystallite size, D ~ 27 nm, thus grows only little to 38 nm in a reaction extended over a period of 96 h. A transient phase, x > 0, which has Bi vacancies, thus primarily grows in (101) and (110) facets by filling-up the vacancies over a duly 6.41 % larger crystal density. If any excess Mn, it segregates over a saturated phase, combines to free Bi, and ultimately forms a stable alloy phase. Small crystallites contain an inbuilt surface Bi-layer (shell), 1-2 nm thickness, in a core-shell of nanoplates (20-60 nm width) as shown in HRTEM images. In a proposed microscopic model, hybridized Mn-d5and Bi-p3electrons (also spins) promptly control the magnetic properties. At 300 K, a maximum coercivity Hc = 9.850 kOe (14.435 kOe at 350 K) thus develops (Hc = 5.010 kOe in the initial) in critical single domains (D ~ 33 nm). A net 72.5 emu-g-1 magnetization turns-up with an enhanced TC= 641.5 K (600.5 K at x ~ 0.05) on an order of enhanced anisotropy constant K1in profound effects of a core-shell structure of small crystallites.

中文翻译：

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小核壳 Mn0.5Bi0.5-Bi (≤ 3 at%) 磁体，用于微晶纳米片的各向异性生长、界面桥接和定制磁性能

二元合金Mn0.5+xBi0.5-x，x≤0.05，是一种极具发展前景的高能量密度无稀土磁性材料（电动机和电力电子的关键模块），具有经济价值和深刻的应用前景。在室温下具有多种用途的磁性。在本文中，我们报告了游离 Bi 在 Mn0.5+xBi0.5-x(x ≤ 0.05) 的小微晶上沉淀时如何扩散回稳定的 Mn0.5+xBi0.5-x，x → 0 ，通过包晶反应，这有助于在小核壳微晶的多个方面优先生长，并具有适当的磁性。在 Ar 气体中以 573 K 的临界温度对反应性纳米粉末进行退火时，它在空位的各向异性通道中缓慢移动。因此，在 96 小时内延长的反应中，初始微晶尺寸 D ~ 27 nm 仅生长到 38 nm。因此，具有 Bi 空位的瞬态相 x > 0 通过在适当大 6.41% 的晶体密度上填充空位而主要在 (101) 和 (110) 晶面上生长。如果任何过量的 Mn，它会在饱和相上偏析，结合以释放 Bi，并最终形成稳定的合金相。如 HRTEM 图像所示，小微晶在纳米板的核壳（20-60 nm 宽）中包含一个内置的表面双层（壳），厚度为 1-2 nm。在提出的微观模型中，杂化的 Mn-d5 和 Bi-p3 电子（也是自旋）迅速控制了磁性。在 300 K 时，在临界单畴（D ~ 33 nm）中产生最大矫顽力 Hc = 9.850 kOe（350 K 时为 14.435 kOe）（初始 Hc = 5.010 kOe）。净 72.5 emu-g-1 磁化强度提高了 TC = 641.5 K（在 x ~ 0 时为 600.5 K。