Investigating the size distributions of Co nanoparticle ensembles is an important problem, which has no straightforward solution. In this work, we use the combination of ⁵⁹Co internal field nuclear magnetic resonance (⁵⁹Co IF NMR) and ferromagnetic resonance (FMR) spectroscopies on a metallic Co nanoparticle sample with a narrow Co nanoparticle size distribution due to encapsulation within the inner channels of carbon nanotubes. High-resolution transmission electron microscopy (TEM) images showed that the nanoparticles can be represented as prolate spheroids, with the majority of particles having an aspect ratio between 1 and 2. This observation has increased the accuracy of superparamagnetic blocking size calculations from Néel relaxation model by introducing the actual volume of the ellipsoids taken from the image processing. ⁵⁹Co IF NMR and FMR experiments conducted under different temperatures allowed us to observe the thermal blocking of superparamagnetic particles in full accordance with the TEM particle volume distribution. This proved that these magnetic resonance techniques can be used jointly for characterization of Co nanoparticles in the bulk of the sample.

中文翻译：

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变温磁共振法研究金属钴纳米粒子的超顺磁行为

研究Co纳米颗粒集合体的尺寸分布是一个重要的问题，尚无直接解决方案。在这项工作中，我们结合使用⁵⁹ Co内部场核磁共振（⁵⁹Co IF NMR）和铁磁共振（FMR）光谱图，归因于由于封装在碳纳米管内部通道内而具有狭窄的Co纳米颗粒尺寸分布的金属Co纳米颗粒样品。高分辨率透射电子显微镜（TEM）图像显示，纳米粒子可以表示为扁长球体，大多数粒子的纵横比在1-2之间。此观察结果提高了根据Néel弛豫模型计算超顺磁阻塞尺寸的准确性通过介绍从图像处理中获取的椭球体的实际体积。⁵⁹在不同温度下进行的Co IF NMR和FMR实验使我们能够完全根据TEM颗粒体积分布观察超顺磁性颗粒的热阻滞。这证明了这些磁共振技术可以共同用于表征大部分样品中的Co纳米颗粒。