Magnetic Properties Of Nanotubes Research Articles

Potential magnetic properties of nanotubes (n, 0) with Klein and Fujita edges

Analytical solutions for localized states of zigzag-type nanotube (NT) fragments with various combinations of Klein and Fujita borders are considered using the Huckel approach. It is shown that the equations for determining molecular orbitals (MOs) in systems with two Klein edges are similar to equations for systems with two Fujita edges. An analytical formula for the energies of all π MOs is obtained for systems that have a Klein edge on one side and a Fujita edge on the other. It is established that these systems have n orbitals with energy α that are localized on the Fujita and Klein edges in dependence on the MO symmetry. The degeneracy of edge orbitals indicates that there is a tendency toward single occupancy of them and to the appearance of spin (magnetic) properties. In addition, the energies of the states of different multiplicity for NT fragments (8, 0) are calculated using the CASSCF approach. It is shown that the ground state has a multiplicity of 9, as was also indicated by estimates obtained using the density functional method (B3LYP). It is concluded that zigzag-type NTs with asymmetric edges have a tendency to exhibit spin properties. It is noted that the construction of nanoscale magnetic materials based on them is very promising.

Highly ordered transition metal ferrite nanotube arrays synthesized by template-assisted liquid phase deposition

Highly ordered spinel ferrite MxFe3−xO4 (M = Ni, Co, Zn) nanotube arrays were synthesized in anodic aluminium oxide (AAO) templates with a pore size of 200 nm by combining a liquid phase deposition (LPD) method with a template-assisted route. The morphology of the transition metal ferrite nanotubes was characterized by electron microscopy (FE-SEM; TEM, SAED and HRTEM) and atomic force microscopy (AFM), whereas their chemical composition was determined by inductive coupling plasma (ICP). The phase purity was studied by X-ray diffraction (XRD) and the magnetic properties of the nanotubes were measured by SQUID measurements. Unlike the deposition of thin film structures, nanotube arrays form within the pores of the AAO templates in a much shorter time due to the attractive interactions between the positively charged AAO and the negatively charged metal complex species formed in the treatment solution. The as-deposited nanotubes are amorphous in nature and can be converted into polycrystalline metal ferrites via a post-synthesis heat treatment which induce the dehydroxylation, crystallization and formation of the spinel structure. The resulting nanotubes are uniform with smooth surfaces and open ends and their wall thickness can be varied from 4 to 26 nm by increasing the deposition time from 1 to 4 h. Significant differences in the magnetic properties of the ferrite nanotubes have been observed and these differences seem to result from the chemical composition, the wall thickness and the annealing temperature of the spinel ferrite nanotubes.

The structural and magnetic properties of Co-doped titanate nanotubes synthesized under hydrothermal conditions

Co-doped titanate nanotubes were prepared from hydrothermal treatment on Co-doped anatase TiO2 powders in a concentrated NaOH aqueous solution and characterized by a variety of techniques. We mainly investigated the structural and magnetic properties of these nanotubes. It was found that the obtained nanotubes might possibly be constructed from H2Ti3O7, their undoped counterpart. The result from Raman spectra showed that Ti–OH bonds existed in the tubular structure. The electron paramagnetic resonance and X-ray photoelectron spectroscopy studies clearly showed that the Co was incorporated into the titanate lattice as Co2+ and substituted for Ti cations sites. Also, from the photoluminescence measurement, the presence of oxygen vacancies was detected in the nanotubes. The vibrating sample magnetometer measurement revealed a clear paramagnetic behavior with weakly ferromagnetic ordering at room temperature. The results suggested that ferromagnetism of the nanotubes was related to the oxygen vacancies and could be suppressed by their quantum size.

Electronic structure of carbon multilayer nanotubes

The integral electron density of states at the Fermi level in carbon multilayer nanotubes, which belong to quasi-one-dimensional systems, has been calculated within the tight-binding approximation. It is shown that the density-of-state functions for nanotubes with 20 or more layers and for quasi-two-dimensional graphites virtually coincide. This agreement explains the successful application of the band theory of quasi-two-dimensional graphite to the description of magnetic properties of nanotubes over a wide temperature range.