Magnetooptics of single and microresonator iron-garnet films at low temperatures

We have investigated the low-temperature behavior of the optical and magneto-optical properties of (Bi, Gd, Al)-substituted yttrium iron-garnet films that are either single or microresonator, i.e. sandwiched between two dielectric Bragg mirrors. It was shown that the magneto-optical properties of the microresonators with a magnetic film core are mainly determined by the properties of the constituent magnetic films. Special attention was paid to the compositions possessing magnetic compensation temperatures. The phenomenon of the temperature hysteresis was found and discussed for several samples. This testifies the fact that the magnetic moment reorientation in a magnetic field occurs by the full cycle of the first-order phase transitions “collinear phase – non-collinear phase – collinear phase”. The Faraday hysteresis curves at around magnetic compensation temperatures are demonstrated to be very informative concerning composition of a sample. In particular, the hysteresis curves measured for the magnetic films on the garnet substrates showed bursts that indicates formation of a transition layer.     

Magnetic Circular Dichroism in Nanomaterials: New Opportunity in Understanding and Modulation of Excitonic and Plasmonic Resonances

The unique capability of magnetic circular dichroism (MCD) in revealing geometry and electronic information has provided new opportunities in exploring the relationship between structure and magneto-optical properties in nanomaterials with extraordinary optical absorption. Here, the representative studies referring to application of the MCD technique in semiconductor and noble metal nanomaterials are overviewed. MCD is powerful in elucidating the structural information of the excitonic transition in semiconductor nanocrystals, electronic transitions in noble metal nanoclusters, and plasmon resonance in noble metal nanostructures. By virtue of these advantages, the MCD technique shows its unrivalled ability in evaluating the magnetic modulation of excitonic and plasmonic optical activity of nanomaterials with varied chemical composition, geometry, assembly conformation, and coupling effect. Knowledge of the key factors in manipulating magneto-optical properties at the nanoscale acquired with the MCD technique will largely boost the application of semiconductor and noble nanomaterials in the fields of sensing, spintronic, nanophotonics, etc.     

Proposal for a magnetic-film memory accessed by combined photon and electron beams

A magnetic-film memory accessed by combined photon and electron beams is proposed. The electron beam is used to heat a selected bit, which results in lowering the switching threshold so that information can be written selectively into that bit by means of an external magnetic field. Reading is accomplished by simultaneously illuminating a bit with an electron and a photon beam. Then a thermally modulated magnetic-optical signal is generated by intensity modulation of the electron beam. This arrangement is advantageous since a high-resolution photon beam and photon deflector are not required. The frequency response for thermally modulating a 1-μm bit is calculated to be ∼500 MHz; the necessary temperature dependence of the magneto-optical coefficient and the coercive force can be obtained by using composite films made from layers having different Curie points. Various magneto-optical configurations are readily devised which yield the value of a bit (one or zero) in terms of the phase (0 or π) between the magneto-optical signal and the electron-beam intensity modulation. The shot noise limited signal-to-noise ratio (SNR) is determined by heating of a bit from the photon beam. It is calculated that for a low-loss magnetooptical material such as EuO a 1-μm bit can be read in 1 μs when illuminated with a 1000-μm photon beam. The base-line temperature rise due to heating from the photon beam can be kept small by using narrow pulses of light (widthsim10^{-11}second), as, for example, from a mode-locked laser.     

Ab-initio study for the correlation effect on the magneto-optical properties of Co-based full Heusler alloys

Magneto-optical (MO) properties of ferromagnetic Co₂YGe full-Heusler alloys (Y = Fe and Mn) are investigated by the first principles electronic structure calculations using the highly accurate FLAPW method within GGA + U approach. The polar magneto-optical Kerr angles are calculated by solving Kubo's linear response formula using the FLAPW eigenstates and eigenfunctions to obtain the optical conductivity by interband transitions. The typical features of polar Kerr rotation of transition metals with two major peaks were obtained while the low energy spectra are enhanced largely at 1-2 eV region compared to GGA results. Detailed electronic structures analysis revealed that this enhancement is due to the decreased interband transitions by reduced diagonal optical conductivity. Results indicate that the MO spectra can be used to determine the appropriate correlation level for the present alloys.     

On some optical properties of magnetic photonic crystals

The features of the eigen polarizations of magnetic photonic crystals for large values both of the parameter of magneto-optical activity and the depth of modulation are investigated. The case when the angle between the direction of the external static magnetic field and the normal to the boundary of the layer is zero is considered. The light transmission through the magnetic photonic crystal layer is solved by Ambartsumian's layer addition modified method. The influence of the depth of modulation, the parameter of magneto-optical activity, and the angle of incidence on the eigen polarizations is studied. A simple geometric method for determination of the Bragg frequencies and the widths of forbidden bands is proposed.     

On the theory of near-field magneto-optical microscopy via plasmonic modes of nanowire

The results of a theory of near-field magneto-optical microscopy with a linear probe scanning the near-surface region of a sample are presented. A cylindrical nanowire supporting surface plasmons is considered as a model of the probe. The polar magneto-optical Kerr effect is studied in scattering of light by near-surface nanowire and magnetic nanodomain. The problem is solved self-consistently in the dipolar interactions of the nanowire with the sample surface and in magnetization-linear approximation of magneto-optics. The near-field magneto-optical response depending on the distance between probe and domain is obtained, and the microscopy resolving power is estimated.     

Nonlinear forward scattering in cesium vapor: experiment with simultaneous scanning of laser frequency and B-field

We present the results of an experimental study of nonlinear magneto-optical rotation in a buffer-gas-free uncoated Cs cell on hyperfine transitions F(g) = 3 --> F(e) = 2, 3, 4 of the D(2) line at high laser irradiance (up to 40 mW/cm(2)). The measurements were done in a forward scattering configuration, with simultaneous linear scanning of laser frequency and magnetic field at different temporal rates. The latter revealed, in a single measurement, the dependences of maximum nonlinear Faraday signal and the corresponding B-field on the laser frequency within the Doppler profile.     

A magnetic and magneto-optical investigation of Co-Pt alloy nanowire arrays

We have investigated the magneto-optical properties of highly ordered Co-Pt alloy nanowire arrays embedded in anodic aluminum oxide templates. The magnetic field-dependent Stokes parameters, Faraday rotation angle and ellipticity were investigated by an in-house magneto-optical measurement system. The extracted hysteresis loops are broadly consistent with magnetic hysteresis loops obtained from the vibrating sample magnetometer. The maximum Faraday rotation angle and ellipticity of these samples were examined as a function of nanowire composition. With an increase of platinum content from 9 at.% to 86 at.% in the as-deposited nanowire arrays, the maximum Faraday rotation angle per length decreases linearly from 1.39 x 10(3) degrees/cm to 1.58 x 10(2) degrees/cm. The maximum ellipticity shows a similar behavior with the composition. These linear relationships suggest a dilution model for the magnetic moment in the alloy nanowires. Our results indicate that magneto-optical measurements comprise an effective and sensitive method for monitoring the behavior of AAO-based magnetic nanowire arrays.     

IEEE Magnetics Society & The IEEE Press call for books

The following topic are dealt with: magnetic actuators; magnetic sensors; magneto-optical recording materials; ferromagnetism; magnetic disk drive technology; magnetic heads; magnetic media; magnetic interfaces; magnetic integration; and magnetic hysteresis.     

Role of magnetic polarons in magnetotransport of phase-separated electron systems: Monte–Carlo simulation

A kinetic Monte–Carlo simulation on magnetotransport behaviors of phase-separated magnetic conduction systems where the magnetic polaron aggregates are mixed with insulating phase is presented. The electron conductance is calculated by the spin-dependent electron tunneling among the magnetic polarons. The magnetotransport behavior as a function of volume fraction of magnetic polarons is simulated, reproducing the co-appearance of the insulating-metallic and ferromagnetic transitions. The metallic-insulating transition at low temperature is revealed. The picture of magnetic polaron aggregation as a mode magnetic insulator may be helpful to understand the magnetotransport behaviors in manganites.     

New method for measurement of complex magnetic permeability in themillimeter-wave range, part II: hexaferrites

Magneto-optical methods were applied for the first time in millimeter wavelength range for characterization of anisotropic ferrites. The principles of the free-space magneto-optical method are presented and the new experimental procedures leading to the determination of millimeter-wave permeability and permittivity in anisotropic ferrite materials are described. The measurements were performed with a computer-controlled W-band (70-120 GHz) quasi-optical-waveguide bridge. A backward-wave oscillator was used as a source of tunable millimeter wave radiation. The oriented Sr-hexaferrite ceramic was selected for the verification of millimeter-wave magneto-optical method. The magneto optical measurements in transverse configuration revealed strong anomalous dispersion in the millimeter-wave refractive index spectrum for Sr hexaferrite, mainly due to the frequency variation of magnetic permeability. Computer simulations revealed a good agreement of measured parameters with known data for Sr hexaferrite. It was shown that the free-carrier absorption (σ~0.05 Ω^-1 cm^-1) and magnetic permeability contribute to the relatively high millimeter-wave losses in hexaferrite ceramics. The frequency dependence of Faraday rotation in the millimeter-wave range was measured, and the experimental results are discussed. The results presented in this paper demonstrate that this new magneto-optical method is capable of providing accurate dielectric and magnetic data in the millimeter-wavelength range     

焊接微缺陷磁光成像检测有限元分析

目的 研究铁磁材料焊接微缺陷的磁光成像规律.方法 运用漏磁检测原理和法拉第磁致旋光效应,建立微缺陷三维有限元模型,分析微缺陷磁光成像过程与磁场之间的关联,研究不同提离值、励磁电流、缺陷宽度、缺陷深度下的磁光成像,以及探索这些因素对磁光图像特征的影响.在此基础上,对最小宽度为0.05 mm的微缺陷进行磁光成像检测实验,并...     

Periodic soliton trains in nonlinear magneto-optical media

The combination of the vector nature (i.e. polarization) of light in materials with nonlinearity can give rise to outstanding phenomena in the transmission of nonlinear optical fields. When the optical medium has been initially altered by a magnetic field, magneto-optical effects introduce additional interesting phenomena such as the possible control of optical signals by a magnetic field. The present work addresses the problem of optical-soliton generation from pulsed radiations interacting with a quasi-resonant magneto-optical medium, under normal Zeeman effect. It is shown that multi-soliton structures can be generated in the magneto-optical medium under specific conditions, these include periodic trains of bright and dark optical solitons having finite temporal periods.     

The magneto-optical properties of thin cobalt films

Experimentally measured magneto-optical properties of magnetic materials are usually analysed using a phenomenological approach in which the permittivity is considered as a skew-symmetric tensor. Measurements of the real and imaginary parts of both the optical and the magneto-optical elements of this sensor in the region 1.0–2.5 eV are presented for a series of seven thin (108-13.4 nm) cobalt films. The prominent features of the results are remarkably consistent from film to film.     

Magneto-optical visualization of metal-loss defects in a ferromagnetic plate: experimental verification of theoretical modeling

Rare-earth iron garnet films with in-plane magnetic anisotropy grown on [111]-oriented substrates are promising for the visualization of magnetic leakage fields in nondestructive evaluation. Such magneto-optical films have to be specifically engineered, and we give an example of this technology. To assess the validity and accuracy of finite-element calculations of a magnetization assembly combined with the physical modeling of the image formation, comparisons between calculated and experimentally obtained magneto-optical images of metal-loss defects have been made. A convincing quantitative agreement is demonstrated. It is shown that both physical and computer modeling techniques allow for a predictive engineering design of the prospective applications and provide greater insight into the method.     

Optical and magnetic properties of ZnCoO layers

Optical and magneto-optical properties of ZnCoO films grown at low temperature by Atomic Layer Deposition are discussed. Strong wide band absorption, with onset at about 2.4 eV, is observed in ZnCoO in addition to Co-related intra-shell transitions. This absorption band is related to Co 2+ to 3+ photo-ionization transition. A strong photoluminescence (PL) quenching is observed, which we relate to Co recharging in ZnO lattice. Mechanisms of PL quenching are discussed.     

Comparison of the Mid-Infrared Magneto-Optical Response of Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As Films Grown by Molecular Beam Epitaxy and Ion Implantation and Pulsed Laser Melting

We have carried out mid-infrared magneto-optical studies of Ga_1−x Mn _x As films grown using two different techniques: low temperature molecular beam epitaxy (LT-MBE) and a combination of ion-implantation and pulsed laser melting (II-PLM). The second method is a high temperature growth technique which minimizes the formation of Mn interstitials. Both samples exhibit a ferromagnetic response with similar Curie temperatures (T _C). The samples show qualitatively similar behavior in below bandgap Faraday and Kerr measurements, which probe the valence band structure of the materials. This suggests that the same mid-infrared transitions are dominating the magneto-optical response of both samples.     

聚焦光斑磁光极克尔磁滞回线的热效应分析

实验设计并组建了一套磁光极克尔磁滞回线测量装置,该装置可以通过改变照射到样品上的激光功率来改变薄膜样品上被聚焦光斑照射的测试点的温度。同时通过计算模拟了激光照射在TbFeCo磁光薄膜上的温度分布情况,得到了薄膜的矫顽力随照射激光功率的变化关系,由此可以确定薄膜的居里温度和补偿温度。为研究磁光薄膜样品在各种温度条件下,磁光性能的变化以及多层磁光薄膜的磁耦合效应提供了有效的手段。     

Bi-Mn合金研究进展

MnBi相具有显著的铁磁性及磁光效应,可用作永磁和磁光存储材料.对Bi-Mn合金进行掺杂可改善合金的性能.一些新的Bi-Mn化合物表现出诱人的特性,如巨磁阻效应、铁电效应等.用外加电场或磁场可影响合金的凝固组织和性能.综述了这几方面的最新研究进展.     

Magneto-optical stokes polarimetry and nanostructured magnetic materials

Stokes parameters fully characterize the polarization state of light in an experimentally accessible manner. Photoelastic modulator (PEM) based Stokes polarimetry offers a very high sensitivity which is particularly suitable for the investigation of the magneto-optical properties of nanostructured magnetic materials. In this paper, we shall describe a robust methodology recently developed by us that utilizes a dual PEM setup. As an example of its application, we report on the magneto-optical characteristics of focused Ga ion beam patterned Fe films. We have investigated Ga ion irradiation of single-layer polycrystalline Fe films deposited on Si3N4 substrates, which allows us to study the effects of ion implantation with minimum added complications. Complemented by structural and other characterization techniques, the absolute measurement of magneto-optical effects through the determination of Stokes parameters has enabled us to effectively separate the various contributions from film thinning due to sputtering, structural modifications and compositional changes caused by Ga incorporation. A comparison is also made between the magneto-optical behavior of patterned thin films and that of anodic aluminum oxide embedded magnetic nanowire arrays.