多壁碳纳米管毡的磁性研究：顺磁迈斯纳效应的证据
Magnetic studies of multi-walled carbon nanotube mats: Evidence for the paramagnetic Meissner effect
摘要：
我们报告磁性测量高达1200 K的多壁碳纳米管垫使用量子设计振动样品磁强计。广泛的磁性数据一致地显示两个铁磁类转变在约1000 K和1275 K，分别。在约1000 K的较低的过渡与Fe杂质相和其饱和磁化强度是在定量协议与Fe浓度由电感耦合等离子体质谱仪测量。另一方面，较高过渡相（$\geq$ 1.0 emu/g）的饱和磁化强度比从Co或CoFe的测量浓度所预期的大大约四个数量级，其具有足够高的居里温度来解释这种高过渡。我们发现，在约1275 K的转变是不符合的铁碳系统的磁性邻近效应和铁磁性的任何碳基材料或磁性杂质，但与顺磁迈斯纳效应由于颗粒超导体中的$π$约瑟夫森结的存在。
英文摘要：
We report magnetic measurements up to 1200 K on multi-walled carbon nanotube mats using Quantum Design vibrating sample magnetometer. Extensive magnetic data consistently show two ferrromagnetic-like transitions at about 1000 K and 1275 K, respectively. The lower transition at about 1000 K is associated with an Fe impurity phase and its saturation magnetization is in quantitative agreement with the Fe concentration measured by an inductively coupled plasma mass spectrometer. On the other hand, the saturation magnetization for the higher transition phase ($\geq$1.0 emu/g) is about four orders of magnitude larger than that expected from the measured concentration of Co or CoFe, which has a high enough Curie temperature to explain this high transition. We show that this transition at about 1275 K is not consistent with a magnetic proximity effect of Fe-carbon systems and ferromagnetism of any carbon-based materials or magnetic impurities but with the paramagnetic Meissner effect due to the existence of $π$ Josephson junctions in a granular superconductor.
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