Exchange coupling and magnetic anisotropy for different concentration of iron based nanoparticles in aligned carbon nanotube arrays

We present results of study of magnetic properties of nanocomposite formed in situ during the synthesis of aligned carbon nanotube (CNT) arrays. CNTs were grown by the atmospheric pressure floating catalyst chemical vapor deposition method. High temperature pyrolysis of ferrocene/xylene solution injected into the quartz tube at high temperature was carried out. By varying the ferrocene content (CF) in the ferrocene/xylene solution we tuned the concentration, location, size, shape and chemical state of iron based catalytic ferromagnetic nanoparticles. The variation of these parameters was reflected in the magnetic properties of the CNT based nanocomposite. In particular, it is shown, that the main interaction mechanism between ferromagnetic nanoparticles for high CF contents is the exchange coupling, while the magnetic anisotropy dominates at low ferrocene concentration. The role of the orientation of the nanotubes is decisive for the observation of magnetic anisotropy. When the alignment is destroyed, the exchange coupling mechanism starts to dominate also for low CF samples. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)