179 research outputs found
Nonlinear magnetotransport in dual spin valves
Recent experimental measurements of magnetoresistance in dual spin valves [A.
Aziz et al., Phys. Rev. Lett. 103, 237203 (2009)] reveal some nonlinear
features of transport, which have not been observed in other systems. We
propose a phenomenological model describing current-dependent resistance (and
giant magnetoresistance) in double spin valves. The model is based on a
modified Valet-Fert approach, and takes into account the dependence of
bulk/interface resistance and bulk/interface spin asymmetry parameters for the
central magnetic layer on spin accumulation, and consequently on charge
current. Such a nonlinear model accounts for recent experimental observations
Current-pulse-induced magnetic switching in standard and nonstandard spin-valves
Magnetization switching due to a current-pulse in symmetric and asymmetric
spin valves is studied theoretically within the macrospin model. The switching
process and the corresponding switching parameters are shown to depend
significantly on the pulse duration and also on the interplay of the torques
due to spin transfer and external magnetic field. This interplay leads to
peculiar features in the corresponding phase diagram. These features in
standard spin valves, where the spin transfer torque stabilizes one of the
magnetic configurations (either parallel or antiparallel) and destabilizes the
opposite one, differ from those in nonstandard (asymmetric) spin valves, where
both collinear configurations are stable for one current orientation and
unstable for the opposite one. Following this we propose a scheme of ultrafast
current-induced switching in nonstandard spin valves, based on a sequence of
two current pulses.Comment: 7 pages, 5 figures; to be published in Phys. Rev.
Hallmarks of mechanochemistry: From nanoparticles to technology
The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).Slovak Grant Agency VEGA 2/0009/11, 2/0043/11Slovak Agency for Science and Development APVV VV-0189-10, VV-0528-11Russian Foundation for Basic Research 10-03-00942a, 12-03-00651aMinistry of Science and Higher education in Poland CUT/c-1/DS/KWC/2008-2012, PB1T09B02330, NN209145136, NN20914893
Influence of the milling parameters on the mechanical work intensity in planetary mills
The formation of ZnSe via a mechanically-induced self-sustaining reaction (MSR) from a Zn/Se mixture showed that only size reduction and mixing of the reactants without product formation occurred during the induction period prior to ignition. Therefore, all mechanical energy supplied by the planetary mill during this time, called the ignition time (t ig), was used exclusively in the activation of the reactants. This system was chosen to study the dependence of t ig on the main parameters characterising the milling intensity of planetary mills. The variation of the ignition time with the process conditions reflected changes in the mechanical dose rate of the planetary mill. A direct relationship between the inverse of the ignition time and the power of the planetary mill was established, which allows the validation of theoretical models proposed in the literature for the energy transfer in milling devices and the comparison of milling equipment efficienciesCSIC No. 2009SK0002Gobierno de España No. MAT2011-2298
Current-induced dynamics of composite free layer with antiferromagnetic interlayer exchange coupling
Current-induced dynamics in spin valves including composite free layer with
antiferromagnetic interlayer exchange coupling is studied theoretically within
the diffusive transport regime. We show that current-induced dynamics of a
synthetic antiferromagnet is significantly different from dynamics of a
synthetic ferrimagnet. From macrospin simulations we obtain conditions for
switching the composite free layer, as well as for appearance of various
self-sustained dynamical modes. Numerical simulations are compared with simple
analytical models of critical current based on linearized
Landau-Lifshitz-Gilbert equation.Comment: 11 pages, 7 figure
Slovac Republic repository of radioactive waste
The Slovac Republic Repository of Radioactive Waste (radwaste) in place Mochovce presents a multi-barrier repository of the surface type designed as an ultimate storage of treated solid and fixed, low-and very low-level radwaste generated during the operation and decommissioning of the nuclear power plants, in research institutes, laboratories and hospitals in the Slovak Republic. The isolation of the radwaste and retardation of the radionuclides are provided by the barrier system of the repository. To assess the complete system and parts of one of the most important barriers – the multi-barrier ultimate shielding of the repository – the model of the ultimate shielding of the repository was designed. The monitoring results of the model “ in situ“ will be applicable for projecting the ultimate shielding of the repository
Theory of superdiffusive spin transport in noncollinear magnetic multilayers
Ultrafast demagnetization induced by femtosecond laser pulses in thin
metallic layers is caused by the outflow of spin-polarized hot electron
currents describable by the superdiffusive transport model. These
laser-generated spin currents can cross the interface into another magnetic
layer and give rise to magnetization dynamics in magnetic spin valves with
noncollinear magnetizations. To describe ultrafast transport and spin dynamics
in such nanostructures we develop here the superdiffusive theory for general
noncollinear magnetic multilayers. Specifically, we introduce an Al/Ni/Ru/Fe/Ru
multilayer system with noncollinear Ni and Fe magnetic moments and analyze how
the ultrafast demagnetization and spin-transfer torque depend on the
noncollinearity. We employ ab initio calculations to compute the spin- and
energy-dependent transmissions of hot electrons at the interfaces of the
multilayer. Taking into account multiple electron scattering at interfaces and
spin mixing in the spacer layer we find that the laser-induced demagnetization
of the Ni layer and magnetization change of the Fe layer strongly depend on the
angle between their magnetizations. Similarly, the spin-transfer torques on the
Ni and Fe layers and the total spin momentum absorbed in the Ni and Fe layer
are found to vary markedly with the amount of noncollinearity.
These results suggest that changing the amount of noncollinearity in magnetic
multilayers one can efficiently control the hot electron spin transport, which
may open a way toward achieving fast, laser-driven spintronic devices.Comment: 14 pages, 9 figure
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