Magnetism in carbon nanostructures is of high scientific interest, which could lead to novel magnetic materials. The magnetic properties of symmetrical and asymmetrical sized small fullerene dimers (C n for n≤50) have been investigated using spin polarized density functional theory. The interaction energies depict that small fullerene cages form stable dimer structures and symmetrical sized fullerene dimers are found more stable than asymmetrical sized dimers. The dimerization of fullerene cages in different modes leads to change in their magnetic properties. The non-magnetic fullerene cages become magnetic after ). The individual cages of dimer structures show ferromagnetic interactions amongst them and resultant magnetic moment strongly depends on the type of inter-connecting bonds. The magnetism may also be explained based on distortion of carbon cages and change in the density of states (DOS) in dimer configuration. The calculations presented show strong possibility of experimental synthesis of small fullerene based magnetic dimers.
The electronic and magnetic properties of carbon nanobuds have been investigated using density functional theory. The carbon nanobuds are formed by attaching smaller fullerenes (C20, C28, C36 and C40) of variable size with (5,5) ACNT and (5,0) ZCNT. Fullerenes interact strongly with CNT surface having binding energies within the range -0.93eV to -4.06eV. The C-C bond lengths near the attachment region increase from the original C-C bond lengths. The relative stabilities of the nanobuds are closely related to C-C bond lengths and bond angles in cycloaddition reaction. Nanobuds formed by bond cycloaddition are energetically most favorable amongst all cycloadditions. The electronic and magnetic properties of nanobuds depend strongly on electronic properties of its building blocks. The attachment of C20 and C40 on CNTs open up the HOMO-LUMO gaps of nanobuds whereas C28 and C36 results in addition of impurity states near the Fermi level. The total magnetic moment of nanobuds vary from 0.28µB to 4.00µB which depend on the nature of bonding between fullerene and CNTs. The results outline the potential of nanobuds as hybrid carbon nanostructures and how their properties can be tuned with the size and type of fullerene attached.
In the present work, we have deduced the fluorescence (ω 1, ω 2, ω 3) and Coster–Kronig (CK)(f 12, f 13, f 23) yields for Sn (Z = 50) and Sb (Z = 51) from the L i (i = 1–3) sub-shell x-ray intensities measured using the energy tunable synchrotron radiation employing the selective photoionization method. For both the elements, yields have been obtained using two sets of theoretical photoionization cross sections based on the non-relativistic Hartree–Fock–Slater (HFS) model and the self-consistent Dirac–Hartree–Fock (DHF) model. In case of Sb, we have obtained a third set of measured yields also by using the experimental photoionization cross sections evaluated from independent measurements of the mass-attenuation coefficients. The experimental yields for Sb are reported for the first time by us. We have compared the present deduced fluorescence and CK yields with the Dirac–Hartree–Slater model based values, the semi-empirical values tabulated by Krause and the earlier reported values. In case of Sn, using the DHF and the HFS model based photoionization cross sections, two sets of present measured L1 sub-shell fluorescence yields (ω 1) are found to be 0.039 ± 0.007 and 0.036 ± 0.003, and the CK yields (f 13) are found to be 0.428 ± 0.107 and 0.405 ± 0.028, respectively. In case of Sb, using three sets of the photoionization cross sections (DHF, HFS and recent experimental values), the ω 1 values are measured to be 0.042 ± 0.007, 0.040 ± 0.004 and 0.047 ± 0.005, and the CK yields are measured to be 0.343 ± 0.085, 0.297 ± 0.021 and 0.247 ± 0.022, respectively. The comparison of these present measured yields with the theoretical values provided a reliable experimental evidence indicating cut-off of the intense L1–L3M4,5 CK transitions at Z = 50.
Magnetic carbon nano-structures have potential applications in the field of spintronics as they exhibit valuable magnetic properties. Symmetrically sized small fullerene dimers are substitutional doped with nitrogen (electron rich) and boron (electron deficient) atoms to visualize the effect on their magnetic properties. Interaction energies suggests that the resultant dimer structures are energetically favorable and hence can be formed experimentally. There is significant change in the total magnetic moment of dimers of the order of 0.5 μ B after the substitution of C atoms with N and B, which can also be seen in the change of density of states. The HOMO-LUMO gaps of spin up and spin down electronic states have finite energy difference which confirm their magnetic behaviour, whereas for non-magnetic doped dimers, the HOMO-LUMO gaps for spin up and down states are degenerate. The optical properties show that the dimers behave as optical semiconductors and are useful in optoelectronic devices. The induced magnetism in these dimers makes them fascinating nanocarbon magnetic materials. K E Y W O R D S magnetism, small fullerenes, substitutional doping 1 | INTRODUCTIONThe discovery of C 60 , among fullerene family, has triggered an interest in the field of carbon nanostructured materials due to their fascinating physical and electronic properties. [1][2][3] An intensive research has been initiated for large and small fullerene derivatives after the large-scale synthesis of C 60 . [1,3,4] Small fullerenes have possible usage in the field of nano-electronics, spin-electronics, molecular devices, superconducting devices, drug delivery, and energy storage owing to their unique physical and chemical properties. [2,[5][6][7][8] C 20 is the smallest fullerene cage that was synthesized using gasphase debromination [9] and was found to be less stable kinetically than higher fullerenes such as C 36 or C 60 due to its strong curvature. [10,11] The carbon cages such as C 32 , C 44 , and C 50 are important because of their large ionization potentials and band gaps. [12] The spectrum of 11.2 μm unidentified infrared band (UIR) indicates that C 24 fullerene cage can be used as a carrier that acts as a useful probe for astrophysical environment. [13] The surface of the fullerenes, depending on its inter-and intra-curvature, determines their stability and electronic properties. The ability of the surface to react with other objects strongly depends on its ability to form chemical bonds. In carbon networks, the substitution of N and B is strongly favorable as they bracket carbon in periodic table. The substitutional doping of N and B in fullerene cage structures leads to increase in their static polarizabilities. [14] The first N doped derivatives of C 60 and C 70 were synthesized using contact-arc vaporization of graphite in the
The geometric, electronic and magnetic properties of strained graphene nanoribbons were investigated using spin polarized calculations within the framework of density functional theory. Cases of compressive stress along the longer axis of a nanoribbon and tensile stress at the midpoint and perpendicular to the plane of the nanoribbon were considered. Significant structural changes were observed including the formation of nanoripples. The calculated electronic and magnetic properties strongly depend on the size and shape of nanoribbons. The tunable magnetic properties of strained nanoribbons can be employed for designing magnetic nano-switches.
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