38 research outputs found
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Subcyclotron Instability of Alfven Eigenmodes due to Energetic Ions in Low Aspect Ratio Plasmas
High-frequency modes with frequencies below the fundamental cyclotron frequency of thermal ions were observed in the National Spherical Torus Experiment (NSTX). Based on the measured spectrum of high-frequency modes they are identified as Compressional Alfven Eigenmodes (CAEs) and Global Alfven Eigenmodes (GAEs). CAEs have similar time evolution as plasma parameters change, while GAEs may intersect due to q-profile relaxation. A theory has been developed to study the properties of these modes. Both types of instabilities are driven by the tangential neutral-beam injection in NSTX. Beam ions excite CAEs/GAEs through the Doppler-shifted cyclotron resonance. The main source for the drive is the velocity space anisotropy of the beam ion distribution function. Simulations of the effect CAEs/GAEs may have on plasma ions indicate that these modes may provide a channel for efficient energy transfer from fast ions directly to thermal ions
Semiconductor Spintronics
Spintronics refers commonly to phenomena in which the spin of electrons in a
solid state environment plays the determining role. In a more narrow sense
spintronics is an emerging research field of electronics: spintronics devices
are based on a spin control of electronics, or on an electrical and optical
control of spin or magnetism. This review presents selected themes of
semiconductor spintronics, introducing important concepts in spin transport,
spin injection, Silsbee-Johnson spin-charge coupling, and spindependent
tunneling, as well as spin relaxation and spin dynamics. The most fundamental
spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling.
Depending on the crystal symmetries of the material, as well as on the
structural properties of semiconductor based heterostructures, the spin-orbit
coupling takes on different functional forms, giving a nice playground of
effective spin-orbit Hamiltonians. The effective Hamiltonians for the most
relevant classes of materials and heterostructures are derived here from
realistic electronic band structure descriptions. Most semiconductor device
systems are still theoretical concepts, waiting for experimental
demonstrations. A review of selected proposed, and a few demonstrated devices
is presented, with detailed description of two important classes: magnetic
resonant tunnel structures and bipolar magnetic diodes and transistors. In most
cases the presentation is of tutorial style, introducing the essential
theoretical formalism at an accessible level, with case-study-like
illustrations of actual experimental results, as well as with brief reviews of
relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure
ChemInform Abstract: Structure and Physical Properties of Compounds R2Ni3Si5 (R: Y, Gd, Tb, Dy, Ho, Er, Tm, Lu)
Onset of Itinerant Ferromagnetism in Cobalt-Nickel Heusler-Type Compounds
The magnetic properties of Co-Ni compounds with MnCu_{2}Al or MgAgAs-type structure (the Heusler phases) were studied. Paramagnetic, ferromagnetic moments, Curie's temperature increase with Co content. The ratio of ordered to paramagnetic moment varies with the Curie temperature following itinerant ferromagnetism models. A metal-insulator transition occurs in the TiCo_{x}Ni_{1-x}Sn series, which causes a more rapid drop of the Curie temperature than in TiCo_{x}Ni_{2-x}Sn solid solutions which remain metallic
Coordination of atoms in structures of ternary compounds of rare earth element-transition element-silicon systems
The authors have analyzed the coordination of the smaller atoms in the structures of known ternary intermetallic compounds, formed in the systems rare-earth element ( R)-transition metal ( M)-silicon, and of some binary compounds (for 94 compositions) with the aid of the Yarmolyuk-Kripyakevich phenomenon; to describe the structure they used the contribution of only the smaller atoms ( M and Si) to the weighted-mean coordination number
Mechanism of Conductivity in n-ZrNiSn Intermetallic Semiconductor Doped with Yttrium Acceptor Impurity
International audienc
Features of the structural, electrokinetic, and magnetic properties of the heavily doped ZrNiSn semiconductor: Dy acceptor impurity
International audienc
Synthesis, electronic transport and magnetic properties of Zr1−xYxNiSn, (x=0–0.25) solid solutions
International audienc