Daisuke Matsunaka

Diameter Dependent Magnetic and Electronic Properties of Single-Walled Carbon Nanotubes with Fe Nanowires

We investigate the electronic and magnetic properties of single-walled carbon nanotubes (SWNTs) filled with Fe nanowires, based on the spin-polarized density functional theory. We find that in the stable structure, the Fe-filled (3,3) and (5,0) SWNTs exhibit semiconducting properties, and the magnetic moment of Fe nanowires inside disappears. On the other hand, the Fe-filled (4,4), (5,5), (6,6) and (6,0) SWNTs, having larger radii, are metallic and exhibit ferromagnetic properties. The corresponding magnetic moment increases with increasing nanotube diameter.

Ab initio study of magnetic and electronic properties of Fe-filled single-walled carbon nanotubes

We investigate the electronic and magnetic properties of a metallic (3, 3) single-walled carbon nanotube (SWCNT) filled with a linear Fe nanowire, based on the ab initio spin-polarized density functional theory. We find that in the stable structure the Fe-filled (3, 3), (5, 0) SWCNTs exhibit semiconducting properties, and the Fe nanowires lose their magnetic moment, while the (4, 4), (5, 5), (6, 6), (6, 0) SWCNTs having larger radius with linear Fe nanowires are metallic, and show magnetic moments.

Dynamical Cluster Approximation in Disordered Systems with Magnetic Impurities

We present a theoretical method to study diluted magnetic semiconductors, beyond the single-site approximation, extending the dynamical cluster approximation (DCA). By the method, we can consider the nonlocal correlations due to disorder and discuss effects of the direct exchange interaction between magnetic impurities on the properties of the itinerant carriers. We apply the method to a three-dimensional cubic lattice system with random localized spins. We show that the strong antiferromagnetic superexchange interaction between nearest-neighbor sites suppresses the polarization of the carrier spins.

Suppression of carrier spin polarization in diluted ferromagnetic semiconductors

We present a theoretical method for studying diluted magnetic semiconductors, extending the dynamical cluster approximation. The precursor effects of the localization and the direct exchange interaction between magnetic impurities can be considered in the method. We apply the method to the two-dimensional square lattice system with random localized spins. We show that the strong antiferromagnetic superexchange interaction between nearest-neighbour sites suppresses the polarization of the carrier spin.

First-principles study of interfacial interaction between carbon nanotube and Al2O3(0001)

In this study, using first-principles calculations, we investigated the interfacial nature between single-walled carbon nanotubes (CNTs) and clean Al2O3(0001) surfaces. The calculation results showed that the adhesive energy of CNTs and clean Al2O3(0001) depends on the diameter of CNTs. The structures of the CNTs adsorbed on Al-terminated Al2O3(0001) do not drastically change from those before adsorbing. C atoms of CNTs interacted with the topmost Al atom of Al2O3(0001) by forming covalent bonding. In the case of the O-terminated Al2O3(0001), small-diameter CNTs have strong interaction, which comes from the opening of CNTs catalytically induced by the O-terminated surface and the subsequent formation of mixed covalent-ionic bonding between C and O atoms. This strong interfacial interaction also leads to significant charge transfer from the CNTs to the O-terminated Al2O3(0001). The strong interfacial interaction of small diameter CNTs with the O-terminated Al2O3(0001) would be a possible mechanism for the ...

Effects of impurities on the magnetic property in copper oxides

Abstract We study effects of the nonmagnetic impurities on the magnetic property in the CuO 2 plane of copper oxides. We calculate the spin susceptibility in the normal state, for the CuO 2 plane with nonmagnetic impurities substituted for Cu atoms, on the basis of the d–p model. We take account of the impurity scattering and the Coulomb interaction at each Cu site within the single-site coherent potential approximation and the fluctuation-exchange approximation, respectively. Our result implies that the nonmagnetic impurities suppress the antiferromagnetic spin fluctuations which mediate the superconductivity in high-temperature superconductors.

The effects of nonmagnetic impurity atoms on the electronic states of CuO2 planes

Abstract We study the effects of nonmagnetic impurities on the electronic states of CuO 2 planes in copper oxides. We calculate the local density of states at the copper sites and the oxygen sites, around the impurities. The local density of states in the CuO 2 plane with the impurities increases or decreases, depending on the energy ω , as compared with those without the impurities. The spatial distribution of the local density of states has an anisotropic shape in the vicinity of the Fermi energy ω ∼ ω F . At ϵ p (p-level) ω ϵ d (d-level), there is a difference in the spatial distribution of the local density of states between the d- and p-electrons, while at other energies, those of the d- and p-electrons are practically the same.

Effects of Oxygen Vacancies on the Electronic States in Copper Oxides

We study effects of an oxygen vacancy on the electronic state of the CuO 2 plane in the normal state, on the basis of the d – p model. We calculate the local density of states at copper sites and oxygen sites around the p x -oxygen vacancy, at T = T c . The spatial distribution has a shape which oscillates along the diagonal directions, reflecting the form of the Fermi surface. We find that another gentle oscillation along the X axis appears in the local density of states of d - and p x -electron, while disappears in that of p y -electron due to the crystal structure.

Theoretical Study of Inter-Planer Ordering of Mg-Based LPSO Structures

To study the physical origin of the periodic arrangement of the quadrople solute-enriched layers in Mg-based LPSO structures, we carry out first-principles calculations of the formation energy of the L12 cluster and investigate effects of phonon on the inter-planer ordering of the solute-enriched layers using the 1-dimensional chain model with mass change. The formation energy of the L12 cluster increases as the period of the LPSO structure decreases. Thus, it is found that the electron-mediated interaction is short-range repulsive. On the other hand, in the case of considerably heavy mass change, the ordering of the mass changes is stabilized by phonons and the energy gain increases with the concentration of the mass changes, i.e., the short LPSO period is favorable. A promising mechanism of the inter-planer ordering of the LPSO structures is the phonon-mediated interaction of the quadrople layers where heavy solute atoms are enriched as the L12 clusters at SFs.

Defects Mechanics; Three-Body Problem of Defects Interaction among Crack, Dislocations and Twin Boundary in Magnesium

Dynamics and statics of defects interaction among crack, dislocations and twin boundary (TB) observed in magnesium were investigated using molecular dynamics and elasticity with the complex stress functions to clarify the effect of long-range elastic stress field. An atomic model containing a crack parallel to (10-11) TB was gradually elongated under KI-mode tension by molecular dynamics simulations. Changing the distance between the crack and the TB, four kinds of crack propagation manners were observed, one of which showed the path transition from the crack to the TB itself by shielding effect of piled-up dislocations around the crack tip. The stress intensity factor of the nanosized crack in bulk is 0.28 MPam1/2, which is smaller than that of crack on the TB. The shielding effect due to the piled-up dislocations drastically decreases stress concentration around the crack tip and the stress intensity factor diminishes down to the 0.22, and thus the crack nucleated from the void nucleation and coalescence on the TB was propagated instead. The elastic stress distributions obtained by the superposition of some complex stress functions suggest that the stress field around the crack tip is disturbed by the localized stress due to the TB in the case of crack closest to TB and also by the back stress due to the piled-up dislocations in the case of crack far from TB.