106 research outputs found
Spin dependent transport of ``nonmagnetic metal/zigzag nanotube encapsulating magnetic atoms/nonmagnetic metal'' junctions
Towards a novel magnetoresistance (MR) device with a carbon nanotube, we
propose ``nonmagnetic metal/zigzag nanotube encapsulating magnetic
atoms/nonmagnetic metal'' junctions. We theoretically investigate how
spin-polarized edges of the nanotube and the encapsulated magnetic atoms
influence on transport. When the on-site Coulomb energy divided by the
magnitude of transfer integral, , is larger than 0.8, large MR effect
due to the direction of spins of magnetic atoms, which has the magnitude of the
MR ratio of about 100%, appears reflecting such spin-polarized edges.Comment: 4 pages, 3 figures, accepted for publication in Synth. Metal
A Theoretical Study on Spin-Dependent Transport of "Ferromagnet/Carbon Nanotube Encapsulating Magnetic Atoms/Ferromagnet" Junctions with 4-Valued Conductances
As a novel function of ferromagnet (FM)/spacer/FM junctions, we theoretically
investigate multiple-valued (or multi-level) cell property, which is in
principle realized by sensing conductances of four states recorded with
magnetization configurations of two FMs; (up,up), (up,down), (down,up),
(down,down). In order to sense all the states, 4-valued conductances
corresponding to the respective states are necessary. We previously proposed
that 4-valued conductances are obtained in FM1/spin-polarized spacer (SPS)/FM2
junctions, where FM1 and FM2 have different spin polarizations, and the spacer
depends on spin [J. Phys.: Condens. Matter 15, 8797 (2003)]. In this paper, an
ideal SPS is considered as a single-wall armchair carbon nanotube encapsulating
magnetic atoms, where the nanotube shows on-resonance or off-resonance at the
Fermi level according to its length. The magnitude of the obtained 4-valued
conductances has an opposite order between the on-resonant nanotube and the
off-resonant one, and this property can be understood by considering electronic
states of the nanotube. Also, the magnetoresistance ratio between (up,up) and
(down,down) can be larger than the conventional one between parallel and
anti-parallel configurations.Comment: 10 pages, 4 figures, accepted for publication in J. Phys.: Condens.
Matte
A theoretical investigation of ferromagnetic tunnel junctions with 4-valued conductances
In considering a novel function in ferromagnetic tunnel junctions consisting
of ferromagnet(FM)/barrier/FM junctions, we theoretically investigate multiple
valued (or multi-level) cell property, which is in principle realized by
sensing conductances of four states recorded with magnetization configurations
of two FMs; that is, (up,up), (up,down), (down,up), (down,down). To obtain such
4-valued conductances, we propose FM1/spin-polarized barrier/FM2 junctions,
where the FM1 and FM2 are different ferromagnets, and the barrier has spin
dependence. The proposed idea is applied to the case of the barrier having
localized spins. Assuming that all the localized spins are pinned parallel to
magnetization axes of the FM1 and FM2, 4-valued conductances are explicitly
obtained for the case of many localized spins. Furthermore, objectives for an
ideal spin-polarized barrier are discussed.Comment: 9 pages, 3 figures, accepted for publication in J. Phys.: Condens.
Matte
Magnetoresistance Effect in Spin-Polarized Junctions of Ferromagnetically Contacting Multiple Conductive Paths: Applications to Atomic Wires and Carbon Nanotubes
For spin-polarized junctions of ferromagnetically contacting multiple
conductive paths, such as ferromagnet (FM)/atomic wires/FM and FM/carbon
nanotubes/FM junctions, we theoretically investigate spin-dependent transport
to elucidate the intrinsic relation between the number of paths and conduction,
and to enhance the magnetoresistance (MR) ratio. When many paths are randomly
located between the two FMs, electronic wave interference between the FMs
appears, and then the MR ratio increases with increasing number of paths.
Furthermore, at each number of paths, the MR ratio for carbon nanotubes becomes
larger than that for atomic wires, reflecting the characteristic shape of
points in contact with the FM.Comment: 7 pages, 3 figures, accepted for publication in Phys. Rev.
Noncommutative Quantum Mechanics and Seiberg-Witten Map
In order to overcome ambiguity problem on identification of mathematical
objects in noncommutative theory with physical observables, quantum mechanical
system coupled to the NC U(1) gauge field in the noncommutative space is
reformulated by making use of the unitarized Seiberg-Witten map, and applied to
the Aharonov-Bohm and Hall effects of the NC U(1) gauge field. Retaining terms
only up to linear order in the NC parameter \theta, we find that the AB
topological phase and the Hall conductivity have both the same formulas as
those of the ordinary commutative space with no \theta-dependence.Comment: 7 pages, no figures, uses revtex4; 8 pages, conclusion changed,
Appendix adde
Spin-Atomic Vibration Interaction and Spin-Flip Hamiltonian of a Single Atomic Spin in a Crystal Field
We derive the spin-atomic vibration interaction and the
spin-flip Hamiltonian of a single atomic spin in a crystal field.
We here apply the perturbation theory to a model with the spin-orbit
interaction and the kinetic and potential energies of electrons. The model also
takes into account the difference in vibration displacement between an
effective nucleus and electrons, \Delta {{\boldmath r}}. Examining the
coefficients of and , we first show that
appears for \Delta {{\boldmath r}}0, while is present
independently of \Delta {{\boldmath r}}. As an application, we next obtain
and of an Fe ion in a crystal field of tetragonal
symmetry. It is found that the magnitudes of the coefficients of
can be larger than those of the conventional spin-phonon interaction depending
on vibration frequency. In addition, transition probabilities per unit time due
to and are investigated for the Fe ion with an
anisotropy energy of , where is an anisotropy constant and
is the component of a spin operator.Comment: 55 pages, 17 figures, to be published in J. Phys. Soc. Jpn. 79 (2010)
No. 11, typos correcte
Submillimeter Wave ESR Study of Spin Gap Excitations in CuGeO3
Transitions between the ground singlet state to the excited triplet state has
been observed in CuGeO3 by means of submillimeter wave electron spin resonance.
The strong absorption intensity shows the break down of the selection rule. The
energy gap at zero field is evaluated to be 570 GHz(2.36 meV) and this value is
nearly identical to the gap at the zone center observed by inelastic neutron
scattering. The absorption intensity shows strong field orientation dependence
but shows no significant dependence on magnetic field intensity. These features
have been explained by considering the existence of Dzyaloshinsky-Moriya (DM)
antisymmetric exchange interaction. The doping effect on this singlet-triplet
excitation has been also studied. A drastic broadening of the absorption line
is observed by the doping of only 0.5 % of Si.Comment: 6 pages, 8figures submitted to J. Phys. Soc. Jp
On plane wave and vortex-like solutions of noncommutative Maxwell-Chern-Simons theory
We investigate the spectrum of the gauge theory with Chern-Simons term on the
noncommutative plane, a modification of the description of the Quantum Hall
fluid recently proposed by Susskind. We find a series of the noncommutative
massive ``plane wave'' solutions with polarization dependent on the magnitude
of the wave-vector. The mass of each branch is fixed by the quantization
condition imposed on the coefficient of the noncommutative Chern-Simons term.
For the radially symmetric ansatz a vortex-like solution is found and
investigated. We derive a nonlinear difference equation describing these
solutions and we find their asymptotic form. These excitations should be
relevant in describing the Quantum Hall transitions between plateaus and the
end transition to the Hall Insulator.Comment: 17 pages, LaTeX (JHEP), 1 figure, added references, version accepted
to JHE
Noncommutative Particles in Curved Spaces
We present a formulation in a curved background of noncommutative mechanics,
where the object of noncommutativity is considered as an
independent quantity having a canonical conjugate momentum. We introduced a
noncommutative first-order action in D=10 curved spacetime and the covariant
equations of motions were computed. This model, invariant under diffeomorphism,
generalizes recent relativistic results.Comment: 1+15 pages. Latex. New comments and results adde
Far-Infrared Spectroscopy in Spin-Peierls Compound CuGeO_3 under High Magnetic Fields
Polarized far-infrared (FIR) spectroscopic measurements and FIR
magneto-optical studies were performed on the inorganic spin-Peierls compound
CuGeO_3. An absorption line, which was found at 98 cm in the dimerized
phase (D phase), was assigned to a folded phonon mode of B symmetry. The
splitting of the folded mode into two components in the incommensurate phase
(IC phase) has been observed for the first time. A new broad absorption
centered at 63 cm was observed only in the axis
polarization, which was assigned to a magnetic excitation from singlet ground
state to a continuum state.Comment: 9 pages multicolREVTeX, 10 figure
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