Investigation of Inkjet Printed Composites Based on Single-Walled Carbon Nanotubes With Superparamagnetic Nanoparticles

Porous-matrix composites comprising single-walled carbon nanotubes (SWCNTs) with bound magnetic nanoparticles (NPs) as filler are interesting multifunctional materials whose electrical and magnetic parameters can be used as hallmarks for identification of a genuine document or a bank note, for example. We have formulated stable functional ink based on commercially available product composed of SWCNTs (76 wt. %) and iron-based NPs (11 wt. %) and deposited them on four different thin sheet materials at a given dosage with the use of specialized inkjet printer. To study the magnetic properties, a high-Tc superconducting quantum interference device (HTS SQUID) was designed and fabricated. The printed samples were magnetized in the weak dc magnetic field (3.0 mT/μ0) and moved in the direction of applied field in close proximity to a SQUID sensor. It was found that peak-to-peak stray magnetic field of a magnetized sample (being proportional to its average magnetization) depends on the type of sheet material on which the ink was printed. The larger is the thickness of the printed layer comprising SWCNTs with magnetic NPs, the lower is the signal. Since iron-based NPs are superparamagnetic due to their small size (mean size ~ 4 nm), the difference in the magnetization may result from the difference in the contribution of exchange interaction between NPs. The performed calculations demonstrated that the decay length of electron wave function characteristic of the magnetization is about seven times larger than that of the hopping conductivity in the composites, thus suggesting the mechanism of indirect exchange interaction between NPs involving SWCNTs.