Currents, Torques, and Polarization Factors in Magnetic Tunnel Junctions

Application of Bardeen's tunneling theory to magnetic tunnel junctions having a general degree of atomic disorder reveals the close relationship between magneto-conduction and voltage-driven pseudo-torque, as well as the thickness dependence of tunnel-polarization factors. Among the results: 1) The torque generally varies as sin theta at constant applied voltage. 2) Whenever polarization factors are well defined, the voltage-driven torque on each moment is uniquely proportional to the polarization factor of the other magnet. 3) At finite applied voltage, this relation predicts significant voltage-asymmetry in the torque. For one sign of voltage the torque remains substantial even when the magnetoconductance is greatly diminished. 4) A broadly defined junction model, called ideal middle, allows for atomic disorder within the magnets and F/I interface regions. In this model, the spin dependence of a state-weighting factor proportional to the sum over general state index of evaluated within the (e.g. vacuum) barrier generalizes the local state density in previous theories of the tunnel-polarization factor. 5) For small applied voltage, tunnel-polarization factors remain legitimate up to first order in the inverse thickness of the ideal middle. An algebraic formula describes the first-order corrections to polarization factors in terms of newly defined lateral auto-correllation scales.Comment: This version no. 3 is thoroughly revised for clarity. Just a few notations and equations are changed, and references completed. No change in results. 17 pages including 4 figure

Time-evolution of the Rule 150 cellular automaton activity from a Fibonacci iteration

The total activity of the single-seeded cellular rule 150 automaton does not follow a one-step iteration like other elementary cellular automata, but can be solved as a two-step vectorial, or string, iteration, which can be viewed as a generalization of Fibonacci iteration generating the time series from a sequence of vectors of increasing length. This allows to compute the total activity time series more efficiently than by simulating the whole spatio-temporal process, or even by using the closed expression.Comment: 4 pages (3 figs included

Unusual Low-Temperature Phase in VO2_2 Nanoparticles

We present a systematic investigation of the crystal and electronic structure and the magnetic properties above and below the metal-insulator transition of ball-milled VO$_2$ nanoparticles and VO$_2$ microparticles. For this research, we performed a Rietveld analysis of synchrotron radiation x-ray diffraction data, O $K$ x-ray absorption spectroscopy, V $L_3$ resonant inelastic x-ray scattering, and magnetic susceptibility measurements. This study reveals an unusual low-temperature phase that involves the formation of an elongated and less-tilted V-V pair, a narrowed energy gap, and an induced paramagnetic contribution from the nanoparticles. We show that the change in the crystal structure is consistent with the change in the electronic states around the Fermi level, which leads us to suggest that the Peierls mechanism contributes to the energy splitting of the $a_{1g}$ state. Furthermore, we find that the high-temperature rutile structure of the nanoparticles is almost identical to that of the microparticles.Comment: 7 pages, 8 figures, 2 table

Decentralised energy futures: The changing emissions reduction landscape

© 2015 The Authors. Published by Elsevier B.V. The world is witnessing an energy revolution as renewables become more competitive and energy security becomes a high priority for an increasing number of countries. This development is changing the point along the supply chain ripe for reducing emissions. Whereas carbon capture and storage (CCS) coupled to coal or gas power production offers the potential to decarbonise the current centralised power systems, this relies on a significant increase in electrification to achieve deep emission reductions beyond the power sector, including industrial emissions and transportation. At the same time there is a trend towards decentralised industrial processes, e.g., driven by cost reductions in decentralised production systems and miniature processing plant. New strategies for reducing emissions from decentralised industrial and energy emission point sources will be increasingly important. This paper evaluates different emission reduction strategies that may be relevant to a decentralised energy and manufacturing future, including increased electrification, energy storage, renewable energy and renewable feedstock. Systemic opportunities or barriers and considerations of policy and decentralised decision-making are examined

Identification of Nicotiana tabacum Linkage Group Corresponding to the Q Chromosome Gene(s) Involved in Hybrid Lethality

BACKGROUND: A linkage map consisting of 24 linkage groups has been constructed using simple sequence repeat (SSR) markers in Nicotiana tabacum. However, chromosomal assignments of all linkage groups have not yet been made. The Q chromosome in N. tabacum encodes a gene or genes triggering hybrid lethality, a phenomenon that causes death of hybrids derived from some crosses. METHODOLOGY/PRINCIPAL FINDINGS: We identified a linkage group corresponding to the Q chromosome using an interspecific cross between an N. tabacum monosomic line lacking the Q chromosome and N. africana. N. ingulba yielded inviable hybrids after crossing with N. tabacum. SSR markers on the identified linkage group were used to analyze hybrid lethality in this cross. The results implied that one or more genes on the Q chromosome are responsible for hybrid lethality in this cross. Furthermore, the gene(s) responsible for hybrid lethality in the cross N. tabacum × N. africana appear to be on the region of the Q chromosome to which SSR markers PT30342 and PT30365 map. CONCLUSIONS/SIGNIFICANCE: Linkage group 11 corresponded to the Q chromosome. We propose a new method to correlate linkage groups with chromosomes in N. tabacum

Representations and KK-theory of Discrete Groups

Let $\Gamma$ be a discrete group of finite virtual cohomological dimension with certain finiteness conditions of the type satisfied by arithmetic groups. We define a representation ring for $\Gamma$, determined on its elements of finite order, which is of finite type. Then we determine the contribution of this ring to the topological $K$-theory $K^*(B\Gamma)$, obtaining an exact formula for the difference in terms of the cohomology of the centralizers of elements of finite order in $\Gamma$.Comment: 4 page

Quantum effects for ballistic transport in spintronic devices

Recent fabrication of atomic precision nanodevices for spintronics greatly boosted their performance and also revealed new interesting features, as oscillating magnetoresistance with number of atomic layers in a multilayered structure. This motivates the need to go beyond the usual theoretical approach of semi-classical continuous layers. Here the simple tight-binding dynamics is used to describe quantum conduction in a multicomponent system with spin-polarized electrodes separated by an ultrathin and atomically coherent non-magnetic spacer (either metallic or insulating). A possibility is indicated for obtaining a huge resonant enhancement of magnetoresistance in such device by a special choice of gate voltage on the spacer element.Comment: 9 pages, 9 figure

High resolution modeling of aperture structure and flow path in rock fracture

Water Dynamics: 3rd International Workshop on Water Dynamics, Sendai, Japan, 16-17 November 200

An Improved Initialization Procedure for the Density-Matrix Renormalization Group

We propose an initialization procedure for the density-matrix renormalization group (DMRG): {\it the recursive sweep method}. In a conventional DMRG calculation, the infinite-algorithm, where two new sites are added to the system at each step, has been used to reach the target system size. We then need to obtain the ground state for a different system size for every site addition, so 1) it is difficult to supply a good initial vector for the numerical diagonalization for the ground state, and 2) when the system reduced to a 1D system consists of an array of nonequivalent sites as in ladders or Hubbard-Holstein model, special care has to be taken. Our procedure, which we call the {\it recursive sweep method}, provides a solution to these problems and in fact provides a faster algorithm for the Hubbard model as well as more complicated ones such as the Hubbard-Holstein model.Comment: 4 pages, 4 figures, submitted to JPS

An Effective Reduction of Critical Current for Current-Induced Magnetization Switching by a Ru Layer Insertion in an Exchange-Biased Spin-Valve

Recently it has been predicted that a spin-polarized electrical current perpendicular-to-plane (CPP) directly flowing through a magnetic element can induce magnetization switching through spin-momentum transfer. In this letter, the first observation of current-induced magnetization switching (CIMS) in exchange-biased spin-valves (ESPVs) at room temperature is reported. The ESPVs show the CIMS behavior under a sweeping dc current with a very high critical current density. It is demonstrated that a thin Ruthenium (Ru) layer inserted between a free layer and a top electrode effectively reduces the critical current densities for the CIMS. An "inverse" CIMS behavior is also observed when the thickness of the free layer increases.Comment: 15 pages with figure