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

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

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Features of the structural, electrokinetic, and magnetic properties of the heavily doped ZrNiSn semiconductor: Dy acceptor impurity

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Synthesis, electronic transport and magnetic properties of Zr1−xYxNiSn, (x=0–0.25) solid solutions

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