Single Balls Research Articles

Easy plane antiferromagnets (AFEP) for applications: Hematite

There are two modes of collective oscillations of spins in AFEP's: a gyrotropical (in relation to magnetic moment) mode with frequencies ω <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1K</inf> and an ungyrotropical one with ω <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2K</inf> . Their strong nonlinear connection gives rise to some effects of technical interest both for cm and mm ranges of microwaves: mixing of oscillations, parallel pumping, biresonance frequency doubling, etc. The influence of magnetoelasic (m.e.) interaction on ω <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1K</inf> is amplified by exchange field H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</inf> : <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\omega_{10}/\gamma)^{2} = H(H + H_{D}) + 2H_{E}H_{mes}(P)</tex> where, for hematite (α-Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> ), H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</inf> = 9.2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Oe and, from our measurements, H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mes</inf> (P)= (0.74 - 6.0p) Oe at T = 300 K, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p\parallel\overrightarrow{H}\perpC_{3}</tex> , and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1 \leq p \leq 1.5 k</tex> bar. Because of this, a performance of simple microwave power piezomodulator for mm range is possible even with a single crystal which is not of high quality ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Delta\omega_{10}/\gamma\sim450</tex> Oe). The "shear" m.e. interaction leads to a strong dependence of the sound velocity in hematite on magnetic field: <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_{s} = V_{scs} [1 - 2H_{E}H_{s}/(\omega_{10}/\gamma)^{2}]^{1/2}</tex> . The field variations of eigenfrequencies of hematite single crystal balls quasielastic oscillations, detected with the help of AFMR, give H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> up to 0.7 Oe.

Nonlinear Confining and Deconfining Forces Associated with the Interaction of Laser Radiation with Plasma

The nonlinear interaction of an intense light wave with an inhomogeneous plasma produces a macroscopic motion. A rigorous treatment of this interaction based on the ponderomotive force description leads to a general equation of motion. In a plasma with collisions and high electron density, the resulting force density can be interpreted as an expression of the radiation pressure. Below special densities there results a nonlinear collisionless force whose direction is toward decreasing density, and which produces a deconfinement. The magnitude of this force has a polarization dependence only in the third-order terms of the spatial dependence of the density. The total deconfining recoil momentum transferred to the inhomogeneous transition layer is evaluated. The theory of the nonlinear collisionless acceleration is used to explain the experimentally observed properties of the fast part of plasmas produced by lasers from isolated single small aluminum balls and thick solid targets.

Sputtered III–V Intermetallic Films

IN the course of investigating methods for the deposition of films of semi-conductive materials, it was found that the antimonides of indium and gallium can be readily deposited by means of cathodic sputtering. Reactive sputtering has been widely used for several decades for formation of films of oxides and certain other compounds1; but there seems to have been little interest in the direct sputtering of compound materials. Kane and Wood attempted to produce a sputtered film of Ag2Te, but obtained rather Ag2−xTe (ref. 2). Recently, work concerned with sputtering yields for gallium antimonide3 and directional patterns formed by sputtering from single crystal balls of indium antimonide has been reported4, but in neither case were properties of the films discussed.

Theoretical and Experimental Investigations of Electron Motions in Alternating Fields with the Aid of Ballistic Models

The motion of electrons and the exchange of energy in ultra-high-frequency transverse and longitudinal fields is investigated theoretically and experimentally by means of ballistic models in which single balls or a beam of balls roll over potential slopes whose gradients change with time. In this way there are represented by models, first a cathode-ray tube, then the Heil two-field generator, and finally the Klystron. As is well known, the motion of electrons in electric fields may be imitated in gravitation models in which the potential fields are represented by surfaces whose heights everywhere correspond to the potential lines. The electrons are replaced by balls which roll over the surfaces. In the case of complicated potential fields, for example, the fields in multiple-grid tubes, a sheet of rubber may be stretched out horizontally. By means of supports located below the rubber sheet, its surface, at places corresponding to the electrodes, may be provided with height adjustments corresponding to the electrode potentials at those places. When the surface tension of the membrane is constant, each point obeys the Laplace differential equation, provided that the surfaces do not have too steep slopes in order that the three-dimensional model can, without great error, be regarded as the equivalent of the two-dimensional electric field. There is a further slight difference because of the fact that the balls cannot be regarded as frictionless sliding mass points, but, through the rolling friction, transform part of their energy of motion into rotation energy.