Spin Polarization and Magneto-Coulomb Oscillations in Ferromagnetic Single Electron Devices

The magneto-Coulomb oscillation, the single electron repopulation induced by external magnetic field, observed in a ferromagnetic single electron transistor is further examined in various ferromagnetic single electron devices. In case of double- and triple-junction devices made of Ni and Co electrodes, the single electron repopulation always occurs from Ni to Co electrodes with increasing a magnetic field, irrespective of the configurations of the electrodes. The period of the magneto-Coulomb oscillation is proportional to the single electron charging energy. All these features are consistently explained by the mechanism that the Zeeman effect induces changes of the Fermi energy of the ferromagnetic metal having a non-zero spin polarizations. Experimentally determined spin polarizations are negative for both Ni and Co and the magnitude is larger for Ni than Co as expected from band calculations.Comment: 4 pages, 3 figures, uses jpsj.sty, submitted to J. Phys. Soc. Jp

Nonequilibrium spin distribution in single-electron transistor

Single-electron transistor with ferromagnetic outer electrodes and nonmagnetic island is studied theoretically. Nonequilibrium electron spin distribution in the island is caused by tunneling current. The dependencies of the magnetoresistance ratio $\delta$ on the bias and gate voltages show the dips which are directly related to the induced separation of Fermi levels for electrons with different spins. Inside a dip $\delta$ can become negative.Comment: 11 pages, 2 eps figure

Negative differential conductance and magnetoresistance oscillations due to spin accumulation in ferromagnetic double-island devices

Spin-dependent electronic transport in magnetic double-island devices is considered theoretically in the sequential tunneling regime. Electric current and tunnel magnetoresistance are analyzed as a function of the bias voltage and spin relaxation time in the islands. It is shown that the interplay of spin accumulation on the islands and charging effects leads to periodic modification of the differential conductance and tunnel magnetoresistance. For a sufficiently long spin relaxation time, the modulations are associated with periodic oscillations of the sign of both the tunnel magnetoresistance and differential conductance

ARCHITECTURAL AND PSYCHOLOGICAL ASPECTS IN OPTIMIZED RADIATION SHIELDING DESIGN FOR SPACE APPLICATIONS

NewSpace bears all the hallmarks of past revolutions in technology. Since we have other examples of exponential growth of specific technologies, we should maximize the economic and engineering potential of this movement by expanding the envelopes for long term crewed habitats in deep space. We should also take an approach that minimizes waste in both design and fabrication as these bases expand. This paper provides a systematic approach to habitats optimized for volume, radiation protection, crew psychology, reusability, affordability, crowd-sourced subsystem design, and expansion. These habitats and systems are designed to be as “future proof” as possible to allow rapid and safe technological advancement within the structures. One of major “showstoppers” of human space exploration is cosmic and solar events radiation. It is a serious problem that may cause cancer and other types of tissue damage and equipment malfunction. It has to be addressed in space vehicles design especially for long-term space exploration missions and future Moon or Mars surface settlements. This paper discusses a unique layered system incorporated into a habitat structure, which may help to reduce the radiation hazard to the crew and interior equipment and systems. The paper also argues that a successful mitigation of radiation impact on human health should be based on a multidisciplinary methodology that also includes psychophysiological approach to the problem. Multiple techniques and practices to minimize psychological stress that may suppress immune system and reduce resistance to cancer, are presented and compared. Conclusions are drawn upon results of those comparisons and a multidisciplinary design concept is proposed to be applied both in long-duration human space exploration missions and in radioactive environment on Earth

Magneto-Coulomb Oscillation in Ferromagnetic Single Electron Transistors

The mechanism of the magneto-Coulomb oscillation in ferromagnetic single electron transistors (SET's) is theoretically considered. Variations in the chemical potentials of the conduction electrons in the ferromagnetic island electrode and the ferromagnetic lead electrodes in magnetic fields cause changes in the free energy of the island electrode of the SET. Experimental results of the magneto-Coulomb oscillation in a Ni/Co/Ni ferromagnetic SET are presented and discussed. Possible applications of this phenomenon are also discussed.Comment: 24 pages Latex, 5 figures in GIF files, style files included. Revised version: some errors are corrected and further discussions are added. To be published in J. Phys. Soc. Jpn. Vol.67 (1998) No.

Temperature dependent transport in suspended graphene

The resistivity of ultra-clean suspended graphene is strongly temperature dependent for 5K<T<240K. At T~5K transport is near-ballistic in a device of ~2um dimension and a mobility ~170,000 cm^2/Vs. At large carrier density, n>0.5*10^11 cm^-2, the resistivity increases with increasing T and is linear above 50K, suggesting carrier scattering from acoustic phonons. At T=240K the mobility is ~120,000 cm^2/Vs, higher than in any known semiconductor. At the charge neutral point we observe a non-universal conductivity that decreases with decreasing T, consistent with a density inhomogeneity <10^8 cm^-2

Proximity to Fermi-surface topological change in superconducting LaO0.54F0.46BiS2

The electronic structure of nearly optimally-doped novel superconductor LaO$_{1-x}$F$_x$BiS$_2$ (${\it x}$ = 0.46) was investigated using angle-resolved photoemission spectroscopy (ARPES). We clearly observed band dispersions from 2 to 6 eV binding energy and near the Fermi level (${\it E}_{\rm F}$), which are well reproduced by first principles calculations when the spin-orbit coupling is taken into account. The ARPES intensity map near ${\it E}_{\rm F}$ shows a square-like distribution around the $\Gamma$(Z) point in addition to electronlike Fermi surface (FS) sheets around the X(R) point, indicating that FS of LaO$_{0.54}$F$_{0.46}$BiS$_2$ is in close proximity to the theoretically-predicted topological change.Comment: 6 pages, 3 figures, + supplemental materia