Defects of various kinds strongly affect local magnetic anisotropy and thus play a crucial role in coercivity in high-performance permanent magnets. In particular, in rare-earth-free permanent magnetic alloys with $L{1}_0$ structure microstructural defects deserve special attention. In this work, we report on the “negative” effect of twin structure, and the “positive” effect of dislocations on the coercivity is clarified in a systematic experimental study of $L{1}_0$-MnAl alloys. We find that the nucleation of magnetization reversal is preferentially activated along the twin boundaries and grows into the twin stripes. This suggests that twin structure reduces the domain wall nucleation field, so that the coercivity decreases by approximately 50% according to the direct comparison of twin-free and twinned magnets. In contrast, dislocations dramatically enhance the coercivity by acting as the pinning center, and a high density of dislocations can modify the dominant coercivity mechanism from nucleation to pinning in severely deformed MnAl magnets. With a decreasing dislocation density, the pinning field remains as a constant while the coercivity reduces monotonously, indicative of the “strong pinning” effect of dislocations on the magnetic domain wall, generating a positive correlation between coercivity and density of dislocation. High coercivity from 424 to 328 kA/m is obtained in deformed and annealed magnets with different densities of dislocations. Thus, the combination of eliminating twin structure and introducing high-density dislocations could overcome the present bottleneck in magnetic performance. This work may inspire avenues for the development of $L{1}_0$ rare-earth-free permanent magnetic alloys, and set up a pathway for accelerating the application process.

中文翻译：

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L10无稀土永磁体：孪晶与位错在Mn-Al磁体中的影响

各种缺陷会严重影响局部磁各向异性，因此在高性能永磁体的矫顽力中起着至关重要的作用。特别是在无稀土永磁合金中$\mathrm{大号}{\mathrm{1个}}_0$结构的微结构缺陷值得特别注意。在这项工作中，我们报道了孪晶结构的“负”效应，并且位错对矫顽力的“正”效应在系统的实验研究中得到了澄清。$\mathrm{大号}{\mathrm{1个}}_0$-MnAl合金。我们发现，磁化反转的成核优先沿孪晶边界被激活并长成孪晶条纹。这表明，孪晶结构减少了畴壁的成核场，因此根据自由孪晶和孪晶磁体的直接比较，矫顽力降低了约50％。相反，位错通过充当钉扎中心显着提高了矫顽力，而高密度的位错可以改变严重变形的MnAl磁体中从成核到钉扎的主要矫顽力机制。随着位错密度的降低，钉扎场保持不变，而矫顽力单调降低，这表明位错在磁畴壁上的“强钉扎”效应，在矫顽力和位错密度之间产生正相关。在具有不同位错密度的变形和退火磁体中，可得到424至328 kA / m的高矫顽力。因此，消除孪晶结构和引入高密度位错的组合可以克服目前的磁性能瓶颈。这项工作可能会激发人们的发展途径。$\mathrm{大号}{\mathrm{1个}}_0$ 不含稀土的永磁合金，并为加速应用过程建立了途径。