Self-Assembly Prepared Millimeter Length Ferromagnetic Carbon Nanotubes with Spin Nontrivial Electronic Transport Properties

Exploring the spin degree of freedom in electronic transport of carbon-based materials, such as carbon nanotubes (CNTs), is of interest from the point of view of materials and applications. However, introducing nonequilibrium spin into CNTs is severely limited by the trivial feature of their intrinsic spin and/or the sophisticated fabrication when extra magnetic electrodes are involved. In this work, we alternatively realize exploration of the spin degree of freedom in CNTs by self-assembled encapsulating ferromagnetic Fe3C grains inside their cavity, which not only gives birth to magnetic CNTs but also enables spin nontrivial electronic transport in these CNTs. The structure, composition, and magnetic properties of these Fe3C-CNTs were characterized. The electronic transport and magnetoresistance properties were investigated by using Au/Fe3C-CNTs/Au sandwich devices. The temperature dependence of resistance shows a fluctuation corresponding to the magnetic moment undulation of Fe3C-CNTs, which indicates participation and non-negligible influences of the encapsulated magnetic grains on the electronic transport. Negative magnetoresistance (NMR) related to the magnetization states of the encapsulated magnetic grains is observed, which clearly differs from the conventional magnetoresistance caused by a magnetic field via weak localization but is consistent with the giant magnetoresistance mechanism. Analysis of the temperature dependence of this NMR reveals a linear relationship between the magnetoresistance change and the magnetization of the encapsulated magnetic grains. These results suggest that the electronic transport is similar to that in the magnetic granular system in our Fe3C-CNTs, which is spin dependent. Moreover, these results demonstrate that integrating magnetic species into CNTs is not only a simple method to obtain magnetic nano-building blocks but also a simple approach to explore spin nontrivial electronic transport in CNTs.