Tuning the magnetic properties of iron-filled carbon nanotubes

Carbon, 2006

The thermal decomposition of ferrocene combined with a catalyst-assisted structuring of a Si-substrate surface is a favourable way to produce Fe-filled carbon nanotubes in good quality and in high yields. In this work we have studied the growth of such aligned filled nanotubes on iron and cobalt pre-coated Si-substrates and their dependence on the deposition time. The nanotube diameter depends on the used catalyst metal on the substrate surface. Magnetization measurements were carried out perpendicular (along tube axis) and parallel to the substrate and show excellent coercivities, a strong uniaxial anisotropy (ratios of H c,per /H c,par up to 6) and high saturation magnetization moments per substrate square. The magnetic behavior has been also interpreted as a function of deposition time and of the catalyst metal on the substrate. These investigations were complemented by X-ray diffraction, which revealed a majority fraction of a-Fe and a small amount of Fe 3 C.

In this work, easily tunable magnetic iron filled multi walled carbon nanotubes were synthesized by catalytic chemical vapor deposition technique (CCVD). Iron incorporated nanoporous silica (Fe/NPS) with different silica/iron atomic ratio was synthesized by hydrothermal technique and used for the production of magnetic multi walled carbon nanotubes (m-MWCNTs). As synthesized iron incorporated nanoporous silica material was characterized by powder X-Ray diffraction techniques (XRD), thermo gravimetric analysis (TGA) and N2 adsorption studies. Crystalline nature and the structural stability of the nanoporous material were studied by XRD and TGA techniques respectively. Specific surface area and the porous nature of the nanoporous silica material were studied by N2 adsorption studies. As synthesized magnetic multi walled carbon nanotubes were characterized by XRD, N2 adsorption studies, HRTEM studies and vibrating sample magnetometer (VSM) techniques. The formation of crystalline nature and tubular structure of m-MWCNTs were confirmed by powder XRD techniques and HRTEM analysis. The tuning of surface area and magnetic properties were performed by varying the catalyst iron atoms concentrations. Less concentrated iron incorporated nanoporous silica (100-Fe/NPS) results high surface area (306 m2/g) and high saturation magnetization (24.5 emu/g) value.

Chemical vapor …, 2006

Ferromagnetic-filled carbon nanotubes are new nanostructured materials with many possible applications. They can be synthesized using the thermal decomposition of metallocenes of the iron triad. Two different methods (solid and liquid source CVD) are suitable for producing, at very high filling rates, filled nanotubes on precoated Si substrates. The diameters of deposited filled nanotubes are particularly dependent on the size of catalyst particles on the substrate, while the lengths depend more on the sublimation and decomposition rate of metallocene. The growth mechanism of filled carbon nanotubes is based on the root growth mode. Multiwalled carbon nanotubes, filled with body-centered cubic Fe, show unusual magnetic properties. Aligned-growth nanotube ensembles can reach coercivities up to 130 mT (bulk iron 0.09 mT). Ferromagnetic-filled carbon nanotubes can be successfully used both as cantilever tips in magnetic force microscopy and as a nanocontainer for new therapies in medicine.

Journal of Applied Physics, 2003

Small, 2019

motivated by a broad range of applications for magnetoresistive devices, optical meta-materials, cell-DNA separators, drug delivery vectors, [7,8] and wave based information transport. [9] Both, the high stability of their magnetic equilibrium state against external perturbations, as well as their robust domain walls, which propagate with velocities faster than the spin wave phase velocity, promote them as appealing candidates for racetrack memory devices and for information transport and processing using spin waves in magnonic applications. Various bottom-up synthesis routes for the preparation of magnetic nanowires exist; including for example electrodeposition based on porous membrane templates [1] and pyrolysis of metal-organic precursors. In particular the pyrolysis of ferrocene allows for the formation of iron-filled carbon nanotubes (FeCNT), i.e., multiwall carbon nanotubes, which contain single-phase single-crystalline iron nanowires, [10-14] where the body-centered cubic iron phase dominates. Furthermore, iron nanowires with various crystal orientations can be found with no prevalent orientation. [13] The diameters of the carbon nanotubes and the embedded iron nanowires are in the range of 30-100 and 10-40 nm, respectively. [13] The magnetization dynamics of individual Fe-filled multiwall carbonnanotubes (FeCNT), grown by chemical vapor deposition, are investigated by microresonator ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) microscopy and corroborated by micromagnetic simulations. Currently, only static magnetometry measurements are available. They suggest that the FeCNTs consist of a single-crystalline Fe nanowire throughout the length. The number and structure of the FMR lines and the abrupt decay of the spin-wave transport seen in BLS indicate, however, that the Fe filling is not a single straight piece along the length. Therefore, a stepwise cutting procedure is applied in order to investigate the evolution of the ferromagnetic resonance lines as a function of the nanowire length. The results show that the FeCNT is indeed not homogeneous along the full length but is built from 300 to 400 nm long single-crystalline segments. These segments consist of magnetically high quality Fe nanowires with almost the bulk values of Fe and with a similar small damping in relation to thin films, promoting FeCNTs as appealing candidates for spin-wave transport in magnonic applications.

physica status solidi (a), 2013

We investigated Fe-phases of iron complexes embedded in nonfunctionalized (as-prepared) and functionalized multi-wall carbon nanotubes (MWCNTs). Mössbauer spectroscopy is a very sensitive tool to study chemical states of iron compounds embedded in MWCNTs. It showed that the chemical treatment of the as-prepared MWCNTs caused release of about 84% of iron and modification of the remaining iron compounds. In as-prepared and carboxylated MWCNTs almost 80 and 75% of iron complexes in a form of Fe 3 C exhibited magnetic ordering even at room temperature, respectively. In MWCNT-COONH 4 only 50% of such iron compounds showed local magnetic ordering. In all cases about 2% of magnetic a-Fe fraction was detected. Through the dc magnetization and transmission electron microscopy (TEM) measurements it was proved that cementite nanoparticles formed agglomerates and their sizes were larger than 10 nm. STM measurements indicated increased homogeneity of the surface electric properties in the case of chemically treated carbon nanotubes.

Materials Research Bulletin, 2008

The filling rate of Fe nanowires in carbon nanotubes (CNTs) was improved by a post-treatment which involved annealing and magnetic separation. The annealing process transformed g-Fe to ferromagnetic a-Fe, resulting in a-Fe-filled CNTs with improved magnetic properties. The Fe-filled CNTs were then separated from those unfilled CNTs due to the different attractive forces under magnetic field. Thermal gravimetric analysis (TGA) revealed that the purity of CNTs was improved after magnetic separation and the filling rate can be up to 40.0 wt.%, which is increased about 8.1% comparing with annealed CNTs. The saturation magnetization of CNTs reached 31.45 emu/g after magnetic separation.

physica status solidi (b), 2004

We have synthesized multiwalled carbon nanotubes (MWNTs) including Fe catalysts by the vapor phase growth method at 950 °C. Different Fe concentrations were obtained by varying the Ar and CO flow rates during the vapor phase growing of the MWNTs. Magnetic properties of the MWNTs with different Fe concentrations were characterized by means of SQUID measurements in the temperature range of 5-300 K. As a result, superparamagnetic behaviors were observed at all the Fe concentrations. The form of the Fe catalysts included in MWNTs was discussed in view of the change of the average magnetic moment and the number of Fe particles with changing Fe concentration.

2012

Physics of The Solid State, 2007

The low-temperature dependences of magnetic characteristics (namely, the coercive force H c , the remanent magnetization M r , local magnetic anisotropy fields H a, and the saturation magnetization M s ) determined from the irreversible and reversible parts of the magnetization curves for Fe3C ferromagnetic nanoparticles encapsulated in carbon nanotubes are investigated experimentally. The behavior of the temperature dependences of the coercive force H c (T) and the remanent magnetization M r (T) indicates a single-domain structure of the particles under study and makes it possible to estimate their blocking temperature T B = 420–450 K. It is found that the saturation magnetization M s and the local magnetic anisotropy field H a vary with temperature as ∼T 5/2.