Long distance propagation of a polarized neutron beam in zero magnetic field

A beam of fully polarized cold neutrons was transported through a zero magnetic field region of 70 m length without loss of polarization. The purpose of this exercise was twofold: firstly, to demonstrate that the new zero-field neutron spin-echo method will work also for very long neutron flight paths; secondly, to prove in the most direct way that the neutron free-flight region of the ILL neutron-antineutron oscillation experiment was indeed sufficiently field-free (“quasifree condition”) by using the neutrons themselves as a magnetometer. To this purpose the residual magnetic field integrals in the long “zero-field” region were measured with a conventional neutron spin-echo method. The overall spin precession angle of the neutrons during their flight through the long zero-field region was found to be less than 2°.     

Theory of self-resonant modes with zero external magnetic field in Josephson tunneling junctions

The effect of self-resonant modes in the absence of external magnetic fields in Josephson junctions is investigated by solving the Josephson equation. The method is based on the assumption of no external magnetic field but includes a dc bias and open-ended cavity boundary conditions. One finds a series of even-mode current singularities in the dc current-voltage characteristics. The method also provides theoretical explanations of the Q-value dependence (Q is the quality value in the resonance cavity) of the current singularities, the behavior of the cutoff voltage, and the maximum height of the first even-mode current singularities as found experimentally.     

Frequency and temperature dependence of ultrasonic attenuation in indium in a transverse magnetic field and in zero field

The frequency and temperature dependence of the electronic attenuation of longitudinal ultrasound in indium along [110] has been measured between 1.5 and 4.2 K in the frequency range 10–90 MHz. The zero-field results are well described by a modified free-electron Pippard expression. As expected from general theory the high-field attenuation was proportional to q ² and showed an anisotropy reflecting the symmetry of the electron distribution. The temperature dependence was found to depend on the direction of the magnetic field in the plane normal to q.     

Propagation of zero sound in superfluid3He-B under magnetic field

We present a theory of zero sound propagation in super fluid³He-B with an order parameter strongly distorted by magnetic field. A general formula of the dispersion relation for arbitrary magnetic field in the collisionless regime is derived within the weak coupling theory and under the assumption of particle-hole symmetry. The Landau parameters are taken into account up toF ₂ ^s andF ₀ ^a . Numerical results for the sound velocity and absorption spectrum are presented. We show that the collective modeJ = 1,J _z = 0 yields a sizable peak in the sound absorption spectrum under weak but finite magnetic field. The quasi-particle excitations under magnetic field also exhibit cusp-like fine structures in the absorption spectrum. We show that the anomalies discovered by Ling et al. and Sounders et al. near the pair breaking edge in theq H geometry consist of theJ = 1,J _z = 0 collective mode and the pair breaking cusps in theJ _z = 0, ±2 channels.     

Effect of magnetic field on the zero valent iron induced oxidation reaction

The magnetic field (MF) effect on the zero valent iron (ZVI) induced oxidative reaction was investigated for the first time. The degradation of 4-chlorophenol (4-CP) in the ZVI system was employed as the test oxidative reaction. MF markedly enhanced the degradation of 4-CP with the concurrent production of chlorides. The consumption of dissolved O₂ by ZVI reaction was also enhanced in the presence of MF whereas the competing reaction of H₂ production from proton reduction was retarded. Since the ZVI-induced oxidation is mainly driven by the in situ generated hydroxyl radicals, the production of OH radicals was monitored by the spin trap method using electron spin resonance (ESR) spectroscopy. It was confirmed that the concentration of trapped OH radicals was enhanced in the presence of MF. Since both O₂ and Fe⁰ are paramagnetic, the diffusion of O₂ onto the iron surface might be accelerated under MF. The magnetized iron can attract oxygen on itself, which makes the mass transfer process faster. As a result, the surface electrochemical reaction between Fe⁰ and O₂ can be accelerated with the enhanced production of OH radicals. MF might retard the recombination of OH radicals as well.     

Spin-glass with short-range interaction in a magnetic field

The properties of spin-glasses with nonmagnetic defects are considered in the vicinity of the transition point in a finite magnetic field, by means of a percolational approach. It is shown that the dependence of the magnetic specific heat C(h) = C(h)–C(o) or of the magnetic susceptibility M(h)/h on field and temperature allows us to define the distribution function of finite clusters with respect to their size. In addition to general formulas resulting from the scaling laws, more detailed formulas are obtained for two model distributions: (a) the Bethe lattice distribution, (b) a special model distribution with arbitrary indices.     

Transient magnetic field of a strip line with a magnetic keeper

The transient magnetic field of a strip line in a memory device with a finite conductivity ground plane and a finite permeability magnetic keeper is studied. The driving source consists of a line current or a uniform current sheet. The waveform of the current is assumed to be piecewise linear. Laplace and Fourier transform methods are used to obtain the field.     

真空磁场热处理对Tb0.3Dy0.7Fe1.95合金磁致伸缩性能的影响

研究了磁场热处理对Tb0.3Dy0.7Fe1.95多晶合金磁致伸缩性能的影响.将定向凝固得到的多晶合金,在真空条件下,加热到居里点附近不同温度,在加磁场下保温一定时间后冷却到室温,测量其磁致伸缩系数,并且进行X衍射分析.实验结果表明,在稍低于居里点的温度,沿垂直于棒的轴线加磁场保温一定时间后冷却,合金的磁致伸缩系数明显提高,沿样品棒轴线的晶体取向有一定程度的改变.     

An undulator with a composite magnetic field

A new type of undulator greatly improved in tunability as compared with a usual undulator, is proposed. The undulator has a composite magnetic field which is a linear superposition of two sinusoidally varying fields with different spatial periods. The wavelength can be changed by varying the field strength of the longer-period component while keeping that of the shorter-period component at the highest possible value. Numerical calculations of the spectral brightness were carried out. The proper ratios between the two spatial periods were found to be 3:1, 5:1 and 7:1.     

Template nanowires for spintronics applications: nanomagnet microwave resonators functioning in zero applied magnetic field

Low-cost spintronic devices functioning in zero applied magnetic field are required for bringing the idea of spin-based electronics into the real-world industrial applications. Here we present first microwave measurements performed on nanomagnet devices fabricated by electrodeposition inside porous membranes. In the paper, we discuss in details a microwave resonator consisting of three nanomagnets, which functions in zero external magnetic field. By applying a microwave signal at a particular frequency, the magnetization of the middle nanomagnet experiences the ferromagnetic resonance (FMR), and the device outputs a measurable direct current (spin-torque diode effect). Alternatively, the nanodevice can be used as a microwave oscillator functioning in zero field. To test the resonators at microwave frequencies, we developed a simple measurement setup.     

Thin resistive film with temperature coefficient of resistance close to zero

A new structure of a thin resistive film based on NiCr with a temperature coefficient of resistance (TCR) close to zero is described. The resistor is formed from two nitrogen-doped NiCr films with a sputtered aluminium film between them. This structure, deposited on glass or alumina substrates, has a sheet resistance of 100 Ω, a TCR value less than ±10×10⁻⁶K⁻¹, low tracking of the TCR on the individual substrates and high long-term stability of the sheet resistance. The deposition process is characterized by high reproducibility of electrical properties. The surface and bulk chemical composition of the films have been monitored by secondary ion mass spectrometry and electron spectroscopy for chemical analysis.     

Low magnetic field measurement with a reversed-fieldelectron-spin-resonance magnetometer

An effective method of measuring low magnetic fields is presented. In this method, the magnetic field direction is reversed periodically so that the effects of external magnetic fields, such as the earth's magnetism, are removed. The usefulness of the method is investigated by using a split coil magnetic field source and an electron-spin-resonance magnetometer. A magnetic field of 10 mT can be measured with an uncertainty of less than 0.2 μT, i.e., 20 ppm     

Thermal instability in a nanofluid layer with a vertical magnetic field

The combined effect of a vertical magnetic field and the boundaries on the onset of convection in an electrically conducting nanofluid layer heated from below is investigated using linear stability theory. The employed model incorporates the effects of Brownian motion and thermophoresis. The boundaries are considered to be either rigid or free. The eigenvalue problem is solved analytically for free–free boundaries and numerically for rigid–rigid and lower-rigid and upper-free boundaries using the Galerkin technique. Numerical results are presented for alumina–water nanofluid.     

Verification of zero pair potential in a magnetic metal by superconductive tunnelling

Tunnelling into superconducting multilayers of lead and iron shows that no electron pairs penetrate an iron film if it is thicker than about 5 Å. This proves that the superconducting order parameter decreases to zero within one or two atomic layers in an iron film in contact with a superconductor.     

Bimetallic cylinder in a pulsed magnetic field

The magnetic field diffusion into a bimetallic cylinder comprising a central rod and the outer shell made of different conducting materials is analytically described. In the case of an external field pulse representing a half-wave B _e = B _msin(πt/T), the cylinder exhibits delamination, which is caused by the shell expansion under the action of a residual magnetic field present in its internal cavity. The pressure of this residual field nonmonotonically depends on the conductivity of the rod.     

A model of magnetostriction interaction in thin double-layer magnetic films of Ni-Fe alloy

Under the assumption that in a double-layer film both layers are equally deformed, the following formula for the magnetostriction energyE = K_{c} sin^{2} alphahas been derived whereK_{c} = (9/40)(2U'U"/U'_{0} + U_{0}")is the coupling constant and α is the angle between the magnetization vectors. This formula is valid if we can neglect interaction with the substrate. The sign of the coupling constant is discussed. It turns out that where the composition of the two layers are different, the value of Kccan be, in some special cases, negative.     

Experiments on interferometric enhanced scattering in a plasma with a nonuniform magnetic field

Results are presented from the first experiments on interferometric enhanced scattering (IES) in a plasma in a nonuniform magnetic field. Measurements of the lower hybrid fluctuations of the plasma density by the IES and rf probe methods in an experimental geometry that models a tokamak configuration are found to be in satisfactory agreement. Pis’ma Zh. Tekh. Fiz. 24, 43–51 (October 26, 1998)