Magnetic properties of filled carbon nanotubes
The remanent state of ferromagnetic nanowires inside CNTs is most often a single domain configuration which is expected for the considered nanowires size. In the case of Fe nanowires the remanent magnetization is aligned along the long nanowire axis, i.e., the magnetic anisotropy is dominated by the shape. High aspect ratio Fe nanowires can be regarded as consisting of two well separated magnetic monopoles located near the two wire ends.
Four individual Fe nanowires inside an FeCNT. Top: SEM image. Bottom: MFM phase image.
In contrast, CNTs filled with iron carbid (Fe3C) reveal a magnetization perpendicular to the CNT axis that can be explained in terms of a strong magnetocrystalline anisotropy.
TEM image of iron carbide (Fe3C) filled CNTs
MFM frequency shift image of two Fe3C-filled CNTs
SEM image of an iron-filled CNT placed at the center of a micro-sized Hall device. Inset: SEM backscattered electron image of the Fe-CNT.
Angular variation of the mean nucleation field < Hn > of a 26 nm diameter single crystalline iron nanowire measured by micro-Hall magnetometry. Each point is the average of 10 sweeps. The line corresponds to the curling model. (K. Lipert et al., Appl. Phys. Lett. 97, 212503 (2010).)
Magnetization reversal in an individual 25 nm iron nanowire measured by cantilever magnetometry. (a) Frequency shift hysteresis loop for an FeCNT affixed to a silicon cantilever. The cantilever frequency at zero field has been subtracted from the data. (b) Detailed view of the hysteretic frequency shift during switching. (c) Micrograph of a single FeCNT attached to the end of a silicon cantilever (top view). (d) High resolution field scan showing the detailed switching behavior. The inset shows a histogram of approximately 150 measurements of the switching fields at 6.3 K. The measurement has been done by P. Banerjee, Ohio State University (Banerjee et al., Appl. Phys. Lett. 96, 252505 (2010)).
Contact:
Dr. Thomas Mühl
Department 'Chemical Vapor Deposition'
Institute for Solid State Research (IFF)
IFW Dresden
D-01171 Dresden, Germany
Phone: +49-351-4659-496
Fax: +49-351-4659-9496
Email: t.muehl(et)ifw-dresden.de
See also:
Iron-filled carbon nanotubes as magnetic force microscopy (MFM) probes