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An analysis of neutron radiation effects on NdFeB permanent magnets.

机译：中子辐射对NdFeB永磁体的影响分析。

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摘要

Radiation-induced demagnetization of permanent magnets can result in the failure of magnet-based devices operating in high-radiation environments. To understand the mechanism underlying radiation-induced demagnetization, NdFeB magnets were irradiated with fast and fast plus thermal neutrons. After irradiation, magnetic flux losses were measured and were shown to increase with the fluence. Compared with samples irradiated only with fast neutrons, the samples exposed to the fast plus thermal neutrons had higher magnetic flux losses, which was attributed to the thermal neutron capture reaction of boron. Hysteresis loops of the NdFeB magnets were analyzed using the Jiles Atherton model and revealed an increase in both the coercivity, and the interaction between the domains in the magnet post irradiation and also a decrease in the local magnetic moments. Full remagnetization of the samples after irradiation was possible, which indicates that structural damage is unlikely to be an important factor in the demagnetization process at these levels of neutron energy and fluence. This also indicated that thermal spikes and domain reversal in the affected areas play an important role in the process.;A Molecular Dynamics (MD) simulation was performed on a cube of iron to obtain a better understanding of the thermal spike mechanism and to get a better idea of the time and length scales involved in the process. The results led to time scales on the order of a hundred femtoseconds and length scales on the order of a few nanometers. Finally, an electronic structure calculation based on density functional theory was performed on NdFeB to characterize the role of defects in magnetism loss. The results of the simulation clearly showed that the change of the magnetization depends on the type of structural defect being introduced. However, it was shown that defects introduced to the perfect structure to mimic the effects of fast and thermal neutrons can lead to an observable change in the magnetization. This agreed with previous experimental observations. The effect of defects on the magnetization is expected to be more pronounced with higher energy and higher flux neutron radiation. Finally, it is recommended that a Monte Carlo simulation be developed to predict magnetism loss as a result of radiation. This model should account for multiple thermal spikes and domain reversals throughout the magnet and should also account for structural damage to the magnet after a certain cutoff in radiation fluence and energy.
机译：辐射引起的永磁体退磁会导致在高辐射环境中运行的基于磁体的设备发生故障。为了理解辐射引起的退磁的机理，用快中子和快中子对NdFeB磁体进行了辐照。辐照后，测量磁通量损耗，并显示出其通量会增加。与仅用快中子辐照的样品相比，暴露于快中子和热中子的样品具有更高的磁通量损失，这归因于硼的热中子捕获反应。使用Jiles Atherton模型分析了NdFeB磁体的磁滞回线，结果表明，矫顽力以及辐照后磁体中各畴之间的相互作用都增加了，局部磁矩也减少了。辐照后样品可能会完全磁化，这表明在这些中子能量和通量水平下，结构破坏不太可能成为退磁过程中的重要因素。这也表明受影响区域中的热尖峰和畴反转在该过程中起着重要作用。;对铁立方体进行了分子动力学（MD）模拟，以更好地了解热尖峰的机理并获得更好地了解过程中涉及的时间和长度范围。结果导致时间尺度为一百飞秒，长度尺度为几纳米。最后，基于密度泛函理论对NdFeB进行了电子结构计算，以表征缺陷在磁损耗中的作用。仿真结果清楚地表明，磁化强度的变化取决于引入的结构缺陷的类型。但是，结果表明，引入到完美结构中以模仿快速中子和热中子效应的缺陷会导致磁化强度发生可观察到的变化。这与以前的实验观察结果一致。预期随着能量和通量中子辐射的增加，缺陷对磁化的影响会更加明显。最后，建议开发一种蒙特卡洛模拟方法，以预测由于辐射引起的磁损耗。该模型应考虑到整个磁体的多个热尖峰和磁畴反转，并且还应考虑在辐射通量和能量的一定截止后对磁体的结构损坏。

著录项

  • 作者

    Samin, Adib J.;

  • 作者单位

    The Ohio State University.;

  • 授予单位 The Ohio State University.;
  • 学科 Mechanical engineering.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 267 p.
  • 总页数 267
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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