Spin and charge polarization around magnetic impurities in metals

Our previously developed trial function scheme has been generalized to investigate the spin and charge polarization around the nearest neighbors of the impurity, and the influence of the polarization on the formation of local moments. While the reduction of impurity moment is mostly due to the charge polarization effect, both spin and charge polarizations together yield a polarized moment which compensates up to 60% of the impurity moment. Special case of cluster with completely compensated moment is also considered.     

粘滞性产生的极化电流对微岛的作用

导出了微岛(w/p_i→0)的垂直粘滞性,运用该粘滞性获得了微岛的静电势函数和岛宽随时间演化的动力学方程。理论分析表明,该粘滞性引起的极化电流对微岛起不稳定作用。进一步的数值分析显示当离子温度较小或离子温度突然下降时,极化电流使微岛快速增长,与实验观测到的结果定性一致。     

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导出了微岛(w/pi→0)的垂直粘滞性,运用该粘滞性获得了微岛的静电势函数和岛宽随时间演化的动力学方程。理论分析表明,该粘滞性引起的极化电流对微岛起不稳定作用。进一步的数值分析显示当离子温度较小或离子温度突然下降时,极化电流使微岛快速增长,与实验观测到的结果定性一致。     

Role of hydrogen in giant spin polarization observed on magnetic nanostructures

We demonstrate that the giant spin contrast observed by scanning tunneling microscopy for double-layer Coislands on Pt(111) is caused by adsorbates at the apex of the Cr-coated W tip. The most likely candidate, in ab initio simulations, is hydrogen. Here, the electron charge is highly polarized by the adjacent Cr layers. The hydrogen adsorption site is shown to change from hollow to on top due to the electric field at the tip apex, created by the tunnel voltage.     

Nanoparticle kinetic effects experimentally observed in a magnetic fluid under a quasi-homogeneous magnetic field

The effect of a quasi-homogeneous external magnetic field on a created and decaying space nanoparticle structure and its distribution in a sample of a magnetic fluid was studied. This space structure was created as a grating by applying an interference field of two crossed Ar laser beams. The magnetic field was formed using two electromagnets and was applied in three main directions of the created nanoparticle grating. The magnetic field oriented parallel to the strips of the grating or perpendicular to the grating plain does not significantly change the shape of it. The magnetic field oriented in the perpendicular direction to the grating plain causes redistribution of the nanoparticles and as a consequence a perpendicular nanoparticle “quasi-grating” arises.     

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利用离子香蕉轨道中心坐标和香蕉轨道平均算符,讨论了磁岛转动引起的沿磁力线电流分布及其对新经典撕裂模演进的影响.结果显示,考虑此电流的影响,当磁岛旋转频率ω=ω*i时,被离子香蕉轨道宽度效应削弱的自举电流驱动项基本恢复;当ω=ω*e时,离子香蕉轨道宽度效应对自举电流驱动项的削弱则加剧.这意味着磁岛转动方向不同时,此沿力线电流能显著增大或减弱离子香蕉轨道宽度效应对自举电流驱动项的削弱作用.     

小磁岛转动引起的沿磁力线电流对撕裂模的影响

利用离子香蕉轨道中心坐标和香蕉轨道平均算符,讨论了磁岛转动引起的沿磁力线电流分布及其对新经典撕裂模演进的影响。结果显示,考虑此电流的影响,当磁岛旋转频率ω=ω_*i 时,被离子香蕉轨道宽度效应削弱的自举电流驱动项基本恢复;当ω=ω_*e时,离子香蕉轨道宽度效应对自举电流驱动项的削弱则加剧。这意味着磁岛转动方向不同时,此沿力线电流能显著增大或减弱离子香蕉轨道宽度效应对自举电流驱动项的削弱作用。     

Compton effect in a magnetic field with allowance for polarization effects

A study is made of the scattering of a plane linearly polarized electromagnetic wave by an electron in a magnetic field. The cross section of the process is obtained separately for the and components of the polarization of the incident and scattered waves. The dependence of the cross section on the spin orientation indicates the possibility of self-polarization of the electrons as a result of the scattering of linearly polarized photons.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 47–51, August, 1980.We are very grateful to Professor A. A. Sokolov for his interest in the work and to A. V. Borisov for discussing the results.     

Parametric decay of a magnetic island structure

It is shown that a spatially periodic magnetic island structure can decay into a tearing mode and long-wavelength magnetohydrodynamic fluctuations. The tearing mode has a linger wavelength than that of the island structure, and the growth rate is proportional to $\text{?}{}^{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}$, where ε is the ratio of the reconnection magnetic flux to the shear field flux in the original structure.     

Evolution of the current density profile associated with magnetic island formation in JT-60U

Evolution of the current density profile associated with magnetic island formation of an m/n=2/1 tearing mode was measured using a motional Stark effect (MSE) diagnostic for the first time in the JT-60U tokamak. With the island growth, the current density profile turned flat at the radial region of the island, followed by an appearance of a hollow structure. As the island shrank, the flat region became narrower, and it finally diminished after the disappearance of the island. The fluctuation of the local poloidal magnetic field from MSE showed a strong correlation with a slow island rotation. This indicates that the observed deformation in the current density profile is localized at the island O point.     

Core polarization and magnetic moment of some odd-mass nuclei around N = 50

The effect of core polarization on the magnetic moment is studied for odd-mass nuclei around $\text{N = 50:}{}^{\mathrm{85,\; 87}}\text{Kr}\text{,}{}^{\mathrm{87,\; 89}}\text{Sr}\text{,}{}^{91}\text{Zr and}{}^{89}\text{Y}$. The calculation is done in the framework of the modified Tamm-Dancoff approximation (MTDA). The ground-state wave function is calculated using the configuration space of p?f$\text{\$}\text{?}$and ?dg$\text{\$}\text{?}$shells. The core polarization correction to the magnetic moment is considerable for all the nuclei, except ⁸⁹Y, and it depends upon the particular form of the interaction. For ⁸⁹Y the last odd proton is in the $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ level and the smallness of the correction is supported by the observed value of the magnetic moment.     

Enhancement of the stabilization efficiency of a neoclassical magnetic island by modulated electron cyclotron current drive in the ASDEX upgrade tokamak

The efficiency of generating a helical current in magnetic islands for the purpose of suppression of neoclassical tearing modes (NTMs) by electron cyclotron current drive (ECCD) is studied experimentally in the ASDEX Upgrade tokamak. It is found that the efficiency of generating helical current by continuous current drive in a rotating island drops drastically as the width 2d of the co-ECCD driven current becomes larger than the island width W. However, by modulating the co-ECCD in phase with the rotating islands O point, the efficiency can be recovered. The results are in good agreement with theoretical calculations taking into account the equilibration of the externally driven current on the island flux surfaces. The result is especially important for large next-step fusion devices, such as ITER, where 2d>W is expected to be unavoidable during NTM suppression, suggesting that modulation capability should be foreseen.     

Oscillations of the magnetic polarization in a Kondo system at finite magnetic fields

The electronic properties of a Kondo impurity are investigated in a magnetic field using linear response theory. The distribution of electrical charge and magnetic polarization are calculated in real space. The (small) magnetic field does not change the charge distribution. However, it unmasks the Kondo cloud and generates a Kondo polarization. The weight of the d-electron components with their magnetic moment up and down is shifted and the compensating moments of the s-electron clouds don’t cancel any longer (a requirement for an experimental detection of the Kondo cloud). In addition to the polarization cloud (of the conduction electrons) an oscillating polarization component with a period of half the Fermi wave length is observed. This represents an internal electronic structure of the Kondo impurity.     

Gravitational effects on the polarization plane

We study the rotation of the polarization plane of an electromagnetic wave due to a gravitational field. An evolution law for the polarization plane is derived in the geometric optics approximation. For the particular case of a Kerr space-time, we obtain the polarization plane rotation for an incident light ray parallel to the Z axis at z = - and for a radially outgoing one. The results are compared with others which have already appeared in the literature.     

Controlling the spin polarization of nanostructures on magnetic substrates

It is shown that, by utilizing spin-selective quantum interference, the spin polarization of nanostructures deposited on a magnetic substrate with a surface state can be strongly modulated locally and energetically by an appropriate structural design. This finding is deduced from state-of-the-art ab initio calculations and interpreted within an analytical model. We present results for hexagonal Cu corrals and mesoscopic triangular Co islands on Co-covered Cu(111). These systems are experimentally feasible, and the effect should be detectable with current technology.     

The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic（FM/OSC/FM） system

From experimental results of spin polarized injection and transport in organic semiconductors(OSCs),we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic(FM/OSC/FM) sandwich structure according to the spin drift-diffusion theory and Ohm’s law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.     

Mean free path effects on the current perpendicular to the plane magnetoresistance of magnetic multilayers

We have carried out an experimental and theoretical study of the magnetoresistance MR(H) in the CPP (current perpendicular to the planes) mode for two types of magnetic multilayers that differ only in the ordering of the magnetic layers: [Co(10 A)/Cu(200 A)/Co(60 A)/Cu(200 A)](N) and [Co(10 A)/Cu(200 A)](N)[Co(60 A)/Cu(200 A)](N). The series resistor model predicts that in the CPP mode MR(H) is independent of the ordering of the layers. Nevertheless, the measured MR(H) curves were found to be completely different for the two cases. Calculations based on a realistic band structure and the Kubo formula show that the results are a consequence of a long mean free path.     

Impact of frustrated singularities on magnetic island evolution

The growth of magnetic islands is explored using the magnetohydrodynamic model in a simple slab system in which the value of the tearing mode stability parameter Delta' can be varied continuously. Unless the system is close to marginal stability reconnection is controlled by Sweet-Parker current layers, whose formation is a consequence of the inherent singular structure of magnetic island equilibria.