Faraday Rotation of Overdense Magnetized Plasma

In this study, we investigate Faraday rotation of electromagnetic waves that are anomalously transmitted through an over‐dense magnetized plasma layer. Here, magnetized plasma indicates that the plasma layer is immersed in a uniform magnetic field. Firstly, normally opaque over‐dense magnetized plasma is shown to be transparent to obliquely incident electromagnetic waves. This high transparency can be achieved by providing conditions for resonant excitations of plasmonic modes. The resonant characteristics of the transmission coefficient of the considered structure are determined and discussed. The conditions under which the magnetized plasma behaves as a complete reflector are also obtained. Faraday rotation is shown to be enhanced under high transparency conditions. The reflected wave also exhibits Faraday rotation and is enhanced under total reflection conditions. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

一种完整测量磁光克尔效应和法拉第效应的方法

详细给出了一种测量完整克尔和法拉弟效应的原理和实验装置。该装置简单可靠,安全由计算机控制。利用傅里叶变换方法,实验系统可以在从０．０１度至几百度的克尔和法拉第旋转角范围内以及在１．５￣６．０ｅＶ的光子能量范围内,准确地测量克尔和法拉第旋转角范围内以及在１．５￣６．０ｅＶ的光子能量范围内,准确地测量克尔和法拉第效应的绝对值。作为实验测量的例子,给出了ＭｎＢｉＡｌ合金薄膜样品和ＧａＰ块状样品的克尔和法     

Giant exciton Faraday rotation in Cd1−xMnxTe mixed crystals

New semiconductor compound Cd_1?xMn_xTe exhibits strong Faraday rotation in the interband region. It is shown by measurements of magneto-optical Kerr effect and reflection in magnetic field that unusually large exciton Zeeman splitting plays an essential role in the observed Faraday rotation. A possible explanation of the observed splitting (corresponding to a “g factor” value up to 100) by exchange interaction of excitons with manganese d states is suggested.     

飞秒光诱导铽镓石榴石晶体中的磁化响应研究

运用时间分辨抽运-探测光谱技术,研究了磁光晶体铽镓石榴石(TGG)在不同椭圆偏振态的飞秒激光脉冲诱导下的极化和磁化响应.研究表明,当仅存在逆法拉第效应时,探测光旋转角信号和椭圆率信号的变化方向与圆偏振抽运光的旋向相关.这是由于圆偏振光在TGG晶体中产生的瞬态有效磁场的方向依赖于圆偏振光的旋向所致.光诱导磁化过程与材料的性质有关,TGG晶体的顺磁特性决定了其自旋弛豫时间为几十飞秒.由于探测光旋转角信号和椭圆率信号的半高全宽均为500 fs左右,加之信号强度随着抽运光脉冲能量密度的增加呈线性增长,表明TGG晶 关键词： 铽镓石榴石晶体 抽运-探测光谱技术 逆法拉第效应     

Magneto-optical polarization spectroscopy with soft X-rays

X-ray magneto-optical polarization spectroscopy is a relatively new ellipsometric technique with which the complete polarization state of X-ray radiation after its interaction with magnetic matter can be measured. This comprises rotation and ellipticity, which fully quantify the lights polarization. Employing this technique, the complete magneto-optical constants in the X-ray regime can directly be obtained, in contrast to the more commonly used intensity-only measurements. The Faraday and magneto-optical Kerr effects, being odd with respect to magnetization reversal, can be used for the examination of ferromagnetic (FM) materials. This we demonstrate here with Faraday and Kerr rotation and ellipticity spectra, measured at the 2p edges of Fe, Co, and Ni. The Voigt effect and magnetic linear dichroism (XMLD), which are even with respect to magnetization reversal, are applied to probe both FM and antiferromagnetic (AFM) materials. Using a new XMLD-reflection spectroscopy we present results obtained on technologically important buried AFM NiO layers. PACS 78.20.Ls; 78.70.Dm; 75.70.-i     

Magneto-optic polar Kerr and Faraday effects in magnetic superlattices

Magneto-optic (MO) effects in magnetic multilayers with periodic regions are discussed assuming normal incidence of polarized waves and polar magnetization (Faraday and polar Kerr effects). From the (4 × 4)-matrix formalism simplified analytical expressions linear in the off-diagonal permittivity tensor element are obtained with no loss in accuracy. The MO effects are expressed as weighted sums of contributions from individual layers. Approximate expressions are given for the case when the thickness of magnetic layers is much smaller than the radiation wavelength. The procedure is illustrated on superlattices consisting of symmetric sandwiches of ultrathin magnetic and non-magnetic metallic layers. Partial support from the Grant Agency of Czech Republic # 202/00/0761 is acknowledged.     

Magnetic field effects on coherent backscattering of light

We have studied the influence of magneto-optical Faraday rotation on coherent backscattering of light experimentally, theoretically and by computer simulations of Monte-Carlo type. The consistency of these three approaches reveals new aspects of the propagation of vector waves in turbid media with and without Faraday rotation. Experimentally, we have demonstrated that the Faraday rotation may almost completely destroy the reciprocity of light paths. However, as shown by the simulations, the cone of coherent backscattering may not only be destroyed but also shifted off the exact backscattering direction, parallel to the magnetic field, as long as the amount of circular polarization is not completely destroyed by the multiple scattering. The relationship between coherent backscattering, depolarization and Faraday rotation are explained by a simple path model of vector waves. This leads to a new characteristic correlation length required to properly describe the influence of Faraday rotation on multiple light scattering. Received 28 January 2000     

Optical studies of spin precession in magnetic two-dimensional electron gases

Magnetic two-dimensional electron gases are studied using time-resolved Kerr and Faraday rotation spectroscopy in the Voigt geometry. The data directly reveal both electron and Mn spin precession in modest transverse fields. Scattering by Mn ions dominates the electron spin relaxation processes in these materials, and prevents the electron gas from acquiring a long-lived spin polarization as observed in non-magnetic structures. Nonetheless, a persistent Mn spin polarization occurs which creates a oscillating magnetic field within the electron gas for hundreds of picoseconds.     

Growth-induced magnetic anisotropy behavior in thin garnet films fabricated by pulsed laser deposition

The effect of target rotation rate on the magneto-optical properties and induced magnetic anisotropy of pulse laser deposition grown Bi:YIG garnets has been investigated. The rotation rate dependence of magnetic properties of thin films has been studied using magneto-optical Faraday rotation combined with magneto-optical Kerr measurement setup. Our results show that decreasing the target rotation rate can also increase the polar coercive field and hence magnetic anisotropy. Also the spectral answer of samples show the capability of use of them in one off optical ranges such as visible, near infrared and far infrared regions.     

Quantum magneto-optics of the graphite family

The optical conductivity of graphene, bilayer graphene, and graphite in quantizing magnetic fields is studied. Both dynamical conductivities, longitudinal and Hall’s, are evaluated analytically. The conductivity peaks are explained in terms of electron transitions. Correspondences between the transition frequencies and the magneto-optical features are established using the theoretical results. We show that trigonal warping can be considered within the perturbation theory for strong magnetic fields larger than 1 T. The semiclassical approach is applied for weak fields when the Fermi energy is much larger than the cyclotron frequency. The main optical transitions obey the selection rule with Δn = 1 for the Landau number n, but the Δn = 2 transitions due to the trigonal warping are also possible. The Faraday/Kerr rotation and light transmission/reflection in quantizing magnetic fields are calculated. Parameters of the Slonczewski-Weiss-McClure model are used in the fit taking the previous de Haas-van Alphen measurements into account and correcting some of them in the case of strong magnetic fields.     

The subwavelength tuned magneto-optical Kerr effect in L1_0-FePt films with perpendicular magnetic anisotropy

For L10-FePt films with strong perpendicular anisotropy covered by arrays of hexagonal close-packed polystyrene spheres(PSSs),fine structures are observed in magneto-optical Kerr rotation spectra in the visible spectral range.The reflection minima are found to be located at the same wavelengths as the Kerr rotation peaks.The Kerr rotation enhancement is attributed to the excitation of both the surface plasmon polariton in the dielectric PSS/metal interface and the guide waves(guide mode)in the PSS array.The two-dimensional PSSs/SiO2/FePt system exhibiting a tunable magneto-optical Kerr effect and a high perpendicular magnetic anisotropy will be helpful for designing and fabricating magneto-optics devices.     

二维磁性光子晶体及其模场分析

利用频域有限差分方法分析了两种二维磁性光子晶体结构(方形和圆形空气孔结构)的模场分布和有效折射率. 结果表明：在该种结构的材料中，原本简并的基模被分为两个不简并的偏振模——左旋模和右旋模，且两种模式的有效折射率不同； 其次，该种结构材料的法拉第旋转角较连续分布的磁光介质有显著增加. 通过选择适当的空气孔参数，方孔结构材料的法拉第旋转角可增大约一个数量级，而圆孔结构可增加4倍左右. 同时发现，当光通过这类材料后偏振态发生了变化，随着法拉第旋转角的增加出射光的椭圆率也在增加. 最后分析了产生这一现象的原因并提出了解决偏振态变化这一问题的方法，即在材料中心处引入缺陷. 关键词： 磁光效应 二维磁性光子晶体 频域有限差分法     

Imprints of a primordial magnetic field upon the cosmic microwave background anisotropy and polarization

We review the imprints that a primordial magnetic field may have left upon the cosmic microwave background (CMB) anisotropy and polarization through Faraday rotation around the time of decoupling. Differential Faraday rotation reduces the degree of linear polarization acquired through anisotropic Thomson scattering. Depolarization reduces the damping due to photon diffusion, which results in an increase of the anisotropy on small angular scales. The effect is significant at frequencies around and below 10 GHz {ie2513-1} whereB ₀ is the present strength of the primordial magnetic field.     

Ellipsometric measurement of magnetooptical nonreciprocal effects

To detect small rotation rates with a ring laser the two counter-propagating beams must be uncoupled. This lock-off can be realized using nonreciprocal optical effects yielding different optical path lengths for the two waves. Usually magnetooptical effects are employed for nonreciprocity. To measure, instead of calculating from optical constants, the magnitude of this nonreciprocal effects an ellipsometric method is proposed. Lock-off elements using Faraday or Kerr effect (polar and transverse, respectively) are treated. First measurements were made on FeNi films.     

Large polarization rotation via atomic coherence

We report significant enhancement of the nonlinear Faraday rotation in optically thick Rb vapor. Polarization rotation angles as large as 10 rad were observed for what is believed to be the first time for sub-Gauss magnetic fields. The use of this effect for high-precision magnetometry is also discussed.     

铁磁薄膜中圆偏振光感应的瞬态磁光Kerr峰的物理起源

使用飞秒时间分辨抽运-探测磁光Kerr光谱技术,实验研究了圆偏振光抽运面内磁化FePt和垂直磁化GdFeCo薄膜的磁化演化动力学,发现在时间延迟零点处均出现瞬态Kerr峰.分析了此Kerr峰的起源,指出此瞬态Kerr峰与铁磁性无关,可能起源于自由电子的顺磁磁化,而顺磁磁化的外磁场来自圆偏振抽运光的逆Faraday效应.基于顺磁磁化模型的计算结果支持此观点.基于此观点,逆Faraday效应感应的磁场脉冲宽度应该与激光脉冲宽度一致.     

MnBi磁性多层膜磁光科尔效应的数值模拟

基于各向异性的平面电磁波传输理论和4×4矩阵法，计算了MnBi，Mn_0.53Bi_0.47，Mn_0.52Bi_0.44Sb_0.04磁性多层膜系列的磁光科尔旋转角、椭圆率随波长、入射角、磁性层厚度变化曲线.计算结果表明，模拟的科尔旋转角、椭圆率随波长变化规律与实验结果吻合很好；在一定波长的垂直入射下，模拟的科尔旋转角、椭圆率随磁性层厚度变化曲线出现科尔谱极大；在磁性层厚度一定的情况下，当入射光以某一角度 关键词： 4×4矩阵法 磁性多层膜 磁光科尔谱 介电张量     

Magnetic and magneto-optical properties of ion-synthesized cobalt nanoparticles in silicon oxide

The magnetic and magneto-optical properties of ion-synthesized cobalt nanoparticles in the amorphous silicon oxide matrix are investigated as a function of the implantation dose. The analysis of the field dependences of the magnetization and the magneto-optical Faraday and Kerr effects demonstrates that, as the ion implantation dose increases, the superparamagnetic behavior of an ensemble of cobalt nanoparticles at room temperature gives way to a ferromagnetic response with the anisotropy characteristic of a thin magnetic film. The magnetization curves for the superparamagnetic and ferromagnetic ensembles of cobalt nanoparticles are simulated to determine their average sizes and the filling density in the irradiated layer of the silicon dioxide matrix. It is revealed that the spectral dependences of the Faraday and Kerr effects for ion-synthesized cobalt nanoparticles differ substantially from those for continuous cobalt films due to the localized excitations of free electrons in the nanoparticles.     

Surface plasmon enhanced giant Faraday effect in graphene

We have theoretically investigated the giant Faraday rotation effect in graphene coupled to metal nanoparticles (MNPs). MNP-induced Faraday rotation effect (MIFRE) results in a giant Faraday rotation angle in high-frequency region where usually no significant Faraday rotation would occur in graphene. Another advantage of MIFRE is the enhanced amplification of the rotating light beam. Furthermore, the MIFRE can be tuned by changing the MNP–graphene distance. The high efficiency and tunability of MIFRE in graphene predict its potential applications in novel graphene-based optical modulators and switches.     

Magnetooptik und elektronische Struktur der magnetisch ordnenden Europiumchalkogenide

The absorption coefficient and the interband Faraday rotation of EuS, EuSe and EuTe thin films have been measured as function of the photon energy (1–6 eV), the temperature (2.7–300 K) and the applied magnetic field (0–11.5 kOe). In addition a magnetic field modulation technique has been developed, with a resolution of 2 ? 10^?4 deg. This allows the measurement of the Faraday rotation in fields of only 100 Oe, which is important for metamagnetic samples with low critical fields. A Kramers-Kronig transformation of the Faraday rotation leads to the circular dichroism and from these two quantities and the optical constants the off-diagonal elements of the conductivity tensor have been computed. From a comparison of this experimental result with values obtained from a modified atomic model, we deduce the character of the involved transitions and the spin polarization of the occupied ground states (4f ⁷,p(anion)). In addition the ratio of exchange splitting to band width of the empty 5d final state can be evaluated. The fine structure of the first main peak is discussed in terms of Kasuya's coupling scheme between the 4f ⁶ multiplett and the excited 5d electron. In the antiferromagnetic EuTe the temperature dependence of the Faraday rotation does not follow the net magnetization of the sample for all photon energies, but some transitions show a “ferromagnetic” behavior. This is interpreted in Slater's model of the magnetic Brillouin zone.