290 research outputs found
Resonant Charge Relaxation as a Likely Source of the Enhanced Thermopower in FeSi
The enhanced thermopower of the correlated semiconductor FeSi is found to be
robust against the sign of the relevant charge carriers. At \,\,70
K, the position of both the high-temperature shoulder of the thermopower peak
and the nonmagnetic-enhanced paramagnetic crossover, the Nernst coefficient
assumes a large maximum and the Hall mobility diminishes to
below 1 cm/Vs. These cause the dimension-less ratio / a
measure of the energy dispersion of the charge scattering time
to exceed that of classical metals and semiconductors by two orders of
magnitude. Concomitantly, the resistivity exhibits a hump and the
magnetoresistance changes its sign. Our observations hint at a resonant
scattering of the charge carriers at the magnetic crossover, imposing strong
constraints on the microscopic interpretation of the robust thermopower
enhancement in FeSi.Comment: 5 pages, 3 figure
Co-development of Firm Foundings and Regional Clusters
ABSTRACT: Although firm foundings and the formation of regional clusters are two processes that have separately attracted a lot of scientific attention during recent years, not much research has been conducted to analyse the interrelation between these two processes. This paper gives some new insights into this relation and a framework is presented into which empirical observations and theoretical considerations can be placed. The core elements are the effects the two processes have on each other in the different stages of cluster formation and development
Crossover from coherent to incoherent scattering in spin-orbit dominated Sr2IrO4
Strong spin-orbit interaction in the two dimensional compound Sr2IrO4 leads
to the formation of Jeff=1/2 isospins with unprecedented dynamics. In Raman
scattering a continuum attributed to double spin scattering is observed. With
higher excitation energy of the incident Laser this signal crosses over to an
incoherent background. The characteristic energy scale of this cross over is
identical to that of intensity resonance effects in phonon scattering. It is
related to exciton-like orbital excitations that are also evident in resonant
X-Ray scattering. The crossover and evolution of incoherent excitations are
proposed to be due to their coupling to spin excitations. This signals a
spin-orbit induced entanglement of spin, lattice and charge degrees of freedoms
in Sr2IrO4.Comment: 20 pages, 7 figure
Improved Arithmetic Performance by Combining Stateful and NonâStateful Logic in Resistive Random Access Memory 1Tâ1R Crossbars
Computing-in-memory (CIM) is a promising approach for overcoming the memory-wall problem in conventional von-Neumann architectures. This is done by performing certain computation tasks directly in the storage subsystem without transferring data between storage and processing units. Stateful and non-stateful CIM concepts are recently attracting lots of interest, which are demonstrated as logical complete, energy efficient, and compatible with dense crossbar structures. However, sneak-path currents in passive resistive random access memory (RRAM) crossbars degrade the operation reliability and require the usage of active 1 Transistorâ1 Resistance (1T-1R) bitcell designs. In this article, the arithmetic performance and reliability are investigated based on experimental measurements and variability-aware circuit simulations. Herein, it is aimed for the evaluation of logic operations specifically with fully integrated 1Tâ1R crossbar devices. Based on these operations, an N-bit full adder with optimized energy consumption and latency is demonstrated by combining stateful and non-stateful CIM logic styles with regard to the specific conditions in active 1Tâ1R RRAM crossbars
Spin-wave stiffness of the Dzyaloshinskii-Moriya helimagnet compounds Fe1âxCoxSi studied by small-angle neutron scattering
The spin wave stiffness was measured by small-angle neutron scattering method in the Dzyaloshinskii-Moriya helimagnet compounds Fe1âxCoxSi with x=0.25,0.30,0.50. It has been shown that the spin wave dispersion in the fully polarized state is anisotropic due to Dzyaloshinskii-Moriya interaction. It is reflected in the neutron scattering pattern as two circles for neutrons obtaining and losing the magnon energy, respectively. The centers of the circles are shifted by the momentum transfer oriented along the applied magnetic field H and equal to the wave vector of the spiral ±ks. The radius of the circles is directly related to the stiffness of spin waves and depends on the magnetic field. We have found that the spin-wave stiffness A change weakly with temperature for each individual compound. On the other hand, the spin-wave stiffness A increases linearly with x in contrast to the x dependences of the critical temperature Tc and the low-temperature ordered moment. Experimentally obtained values of the stiffness A approve quantitative applicability of the Bak-Jensen model for the compounds under study
The mechanically induced structural disorder in barium hexaferrite, BaFe12O19, and its impact on magnetism
The response of the structure of the M-type barium hexaferrite (BaFe12O19) to mechanical action through high-energy milling and its impact on the magnetic behaviour of the ferrite are investigated. Due to the ability of the Fe-57 Mossbauer spectroscopic technique to probe the environment of the Fe nuclei, a valuable insight on a local atomic scale into the mechanically induced changes in the hexagonal structure of the material is obtained. It is revealed that the milling of BaFe12O19 results in the deformation of its constituent polyhedra (FeO6 octahedra, FeO4 tetrahedra and FeO5 triangular bi-pyramids) as well as in the mechanically triggered transition of the Fe3+ cations from the regular 12k octahedral sites into the interstitial positions provided by the magnetoplumbite structure. The response of the hexaferrite to the mechanical treatment is found to be accompanied by the formation of a non-uniform nanostructure consisting of an ordered crystallite surrounded/separated by a structurally disordered surface shell/interface region. The distorted polyhedra and the non-equilibrium cation distribution are found to be confined to the amorphous near-surface layers of the ferrite nanoparticles with the thickness extending up to about 2 nm. The information on the mechanically induced short-range structural disorder in BaFe12O19 is complemented by an investigation of its magnetic behaviour on a macroscopic scale. It is demonstrated that the milled ferrite nanoparticles exhibit a pure superparamagnetism at room temperature. As a consequence of the far-from-equilibrium structural disorder in the surface shell of the nanoparticles, the mechanically treated BaFe12O19 exhibits a reduced magnetization and an enhanced coercivity.DFG/SPP/1415APVV/0528-11VEGA/2/0097/1
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