Kletetschka Gunther, Inoue Yoku, Lindauer Jan, Hůlka Zdeněk
Institute of Geology, Czech Academy of Sciences, Rozvojova 269, Prague, Czech Republic.
Department of Applied Geophysics, Charles Univ, Albertov 6, Prague, Czech Republic.
Sci Rep. 2019 Feb 22;9(1):2551. doi: 10.1038/s41598-019-39325-9.
Multiwall carbon nanotubes (MWCNTs) fabricated by chemical vapor deposition contain magnetic nanoparticles. While increasing frequency of electromagnetic field (EMF) exposure (up to <10 kHz) of MWCNTs resulted in slight induced magnetization decrease due to skin effect of the conducting carbon, we discovered that higher frequencies (>10 kHz) contained an exponential magnetization increase. We show that puzzling magnetization increase with decreasing magnetic field amplitude (less than 0.5 A/m for 512 kHz) is due to matching the field amplitudes of the magnetic nanoparticles inside nanotubes. This observation reveals a possibility of magnetic tunneling in MWCNTs (change of magnetic state of blocked magnetic moments). This interpretation is supported by observation of unblocking larger magnetic remanence (MR) portion from MWCNTs with progressively smaller amplitude of oscillating magnetic field.
通过化学气相沉积法制备的多壁碳纳米管（MWCNTs）含有磁性纳米颗粒。虽然随着多壁碳纳米管暴露于电磁场（EMF）的频率增加（高达<10 kHz），由于导电碳的趋肤效应，导致感应磁化强度略有下降，但我们发现更高频率（>10 kHz）时磁化强度呈指数增加。我们表明，随着磁场幅度减小（对于512 kHz，小于0.5 A/m）出现的令人费解的磁化强度增加，是由于纳米管内磁性纳米颗粒的场幅度匹配所致。这一观察结果揭示了多壁碳纳米管中存在磁隧道效应（被阻挡磁矩的磁状态变化）的可能性。随着振荡磁场幅度逐渐减小，从多壁碳纳米管中释放出更大比例的剩余磁化强度（MR），这一观察结果支持了上述解释。
