78 research outputs found
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
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
Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe_4N, and Half-Metallic Ferromagnet: A Systematic Analysis
We theoretically analyze the anisotropic magnetoresistance (AMR) effects of
bcc Fe (+), fcc Co (+), fcc Ni (+), FeN (-), and a half-metallic
ferromagnet (-). The sign in each ( ) represents the sign of the AMR ratio
observed experimentally. We here use the two-current model for a system
consisting of a spin-polarized conduction state and localized d states with
spin--orbit interaction. From the model, we first derive a general expression
of the AMR ratio. The expression consists of a resistivity of the conduction
state of the spin ( or ), , and resistivities due to s--d scattering processes from the
conduction state to the localized d states. On the basis of this expression, we
next find a relation between the sign of the AMR ratio and the s--d scattering
process. In addition, we obtain expressions of the AMR ratios appropriate to
the respective materials. Using the expressions, we evaluate their AMR ratios,
where the expressions take into account the values of of the respective materials. The evaluated AMR
ratios correspond well to the experimental results.Comment: 17 pages, 12 figures, to be published in J. Phys. Soc. Jpn, minor
mistakes corrected, final versio
Reproducible mini-slump test procedure for measuring the yield stress of cementitious pastes
The mini-slump test is a fast, inexpensive and widely adopted method for evaluating the workability of fresh cementitious pastes. However, this method lacks a standardised procedure for its experimental implementation, which is crucial to guarantee reproducibility and reliability of the test results. This study investigates and proposes a guideline procedure for mini-slump testing, focusing on the influence of key experimental (mixing and testing) parameters on the statistical performance of the results. The importance of preparation of always testing at the same time after mixing, testing each batch once rather than conducting multiple tests on a single batch of material, is highlighted. A set of alkali-activated fly ash-slag pastes, spanning from 1 to 75 Pa yield stresses, were used to validate the test method, by comparison of calculated yield stresses with the results obtained using a conventional vane viscometer. The proposed experimental procedure for mini-slump testing produces highly reproducible results, and the yield stress calculated from mini-slump values correlate very well with those measured by viscometer, in the case of fresh paste of pure shear flow. Mini-slump testing is a reliable method that can be utilised for the assessment of workability of cements
Thermoresponsive Fluorescent Water-Soluble Copolymers Containing BODIPY Dye: Inhibition of H-Aggregation of the BODIPY Units in Their Copolymers by LCST
Polymer reaction of poly(p-phenylene-ethynylene) by addition of decaborane: modulation of luminescence and heat resistance
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