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.     

New developments in ionized-cluster beam and reactive ionized-cluster beam deposition techniques

Ionized-cluster beam (ICB) and reactive ionized-cluster beam (R-ICB) deposition techniques are described from the standpoint of the ion-based technique, as applied to the production of thin film devices. In ICB deposition, clusters (macroparticles consisting of approximately 10³ atoms loosely coupled together) instead of atomic or molecular particles are used after ionization, resulting in a remarkable improvement of epitaxial film growth and of the quality of deposited films with strong adhesion. This paper describes in detail the influences of the ion content and the acceleration voltage on nucleation and film properties. MnBi films as magneto-optical memories and ZnO epitaxial films as optical devices are discussed as practical applications of the ICB and R-ICB deposition techniques.     

Intensity, polarization, and phase information in optical disk systems

Digital information in optical data storage systems can be encoded in the intensity, in the polarization state, or in the phase of a carrier laser beam. Intensity modulation is achieved at the surface of the storage medium either through destructive interference from surface-relief features (e.g., CD or DVD pits) or through reflectivity variations (e.g., alteration of optical constants of phase-change media). Magneto-optical materials make use of the polar magneto-optical Kerr effect to produce polarization modulations of the focused beam reflected from the storage medium. Both surface-relief structures and material-property variations can create, at the exit pupil of the objective lens of the optical pickup, a phase modulation (this, in addition to any intensity or polarization modulation or both). Current optical data storage systems do not make use of this phase information, whose recovery could potentially increase the strength of the readout signal. We show how all three mechanisms can be exploited in a scanning optical microscope to reconstruct the recorded (or embedded) data patterns on various types of optical disk.     

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     

伽马射线辐照对掺铅石英光纤的磁光特性影响

研究了伽马射线辐照对掺铅石英光纤磁光特性的影响。实验结果表明: 掺铅石英光纤样品辐照前, 在660、808、980、1310和1550 nm波长处的费尔德常数分别为3.093、1.676、1.240、0.705和0.538 rad/(T•m), 均高于单模光纤的费尔德常数, 且费尔德常数随着波长的增加而减小, 尤其在 660 nm, 相比较单模光纤, 掺铅石英光纤样品费尔德常数提高了20.82%。经伽马射线辐照后, 掺铅石英光纤样品的费尔德常数随着辐照剂量的增加而增大, 尤其在 5 kGy 剂量, 其费尔德常数增加了41.94%, 而单模光纤仅增加了33.04%。掺铅石英光纤通过掺杂及辐照的手段提高了费尔德常数, 在大电流传感领域具有重要意义。     

磁光透明陶瓷的研究进展

磁光材料是指从紫外到红外波段具有磁光效应的光功能材料, 按照材料的类型可将其分为磁光玻璃、磁光晶体、磁光透明陶瓷等。其中, 磁光透明陶瓷是近年来出现的一种新型磁光介质材料, 具有高Verdet常数、大尺寸、高热导率、高激光损伤阈值等优点, 因而是用于高功率激光器中法拉第隔离器最理想的材料之一。目前已经报道的磁光透明陶瓷材料主要包括铽镓石榴石(Tb₃Ga₅O₁₂, TGG)陶瓷、铽铝石榴石(Tb₃Al₅O₁₂, TAG)陶瓷以及一些倍半氧化物陶瓷, 如氧化铽(Tb₂O₃)陶瓷、氧化钬(Ho₂O₃)陶瓷、氧化镝(Dy₂O₃)陶瓷等。本文首先介绍了几种常见的磁光效应, 详细阐述了法拉第效应和克尔效应的基本原理。着重对几种磁光透明陶瓷材料的研究进展、材料性能、应用前景进行了综述和介绍, 并对这几种磁光透明陶瓷的性能进行了比较和分析, 指出了它们存在的问题和今后的研究方向。     

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.     

Effect of rapid quenching on the magnetic and structural properties of Bi-MnBi composites

Rapid quenching of hypereutectic Bi-Mn alloys with compositions ranging from Bi-1.5wt% Mn (Bi-5 at% Mn) to Bi-20 wt% Mn (Bi-50 at% Mn) was carried out to achieve an optimum constitution of the ferromagnetic MnBi phase. Microstructural investigations by optical and electron microscopy techniques revealed the presence of very fine MnBi particles in the as-spun samples. The results of the microstructural and thermal analysis studies have indicated that it is possible to achieve control over the size and amount of the ferromagnetic phase by melt spinning. Some initial results of magnetic properties of melt-spun ribbons are also presented.     

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.     

An electron microscopic study on MnBi thin films

The structure and orientation of MnBi thin films prepared by sequential evaporation of bismuth and manganese on glass substrates were studied by transmission electron microscopy and electron diffraction. Results indicate that these films develop a preferred orientation with thec-axis perpendicular to the film plane. This preferred orientation is due to the formation of MnBi from a highly oriented bismuth layer, i.e., a layer with thec-axis perpendicular to the film plane. Trace amounts of elemental bismuth, manganese and MnO are found in these MnBi films. There is evidence of close parallel alignment between the MnBi and the bismuth lattices.     

MnBi films for magnetooptic recording

Progress made during the past years in the area of magnetooptic data storage by the computer industry has been most impressive. Many material media and physical phenomena have been developed for this particular application. It now appears that a large capacity (gsim 10^{10}bits) magnetooptic data store possessing major advantages over the conventional recording techniques could be developed. Of the many materials and techniques advanced to date, the use of thin films of MnBi for thermomagnetic writing, erasing, and magnetooptic reading has received particularly intensive study because of the many unique properties of this film medium. In order to provide an assessment of the potential of this medium for optical memory application, we have included in this review the pertinent material physical properties of MnBi; the memory characteristics in regard to read, write, and erase operation; the physical process involved in the writing and erasure by thermomagnetic technique; the technique for detection of written information; and the utilization of this medium for magnetic holographic storage. Emphasis is given to the material properties and physical phenomena, rather than the systems considerations in using MnBi films for optical memory.     

Analysis of Faraday effect in multimode tellurite glass optical fiber for magneto-optical sensing and monitoring applications

The design and fabrication of a tellurite glass multimode optical fiber for magneto-optical applications are presented and discussed. The analysis of the polarization shows that an optical beam, linearly polarized at the fiber input, changes to elliptically polarized with an ellipticity of 1∶4.5 after propagating down the fiber. However, the elliptical distribution remains unchanged with or without an applied magnetic field, demonstrating that no circular dichroism occurs within the fiber. The Verdet constant of the tellurite glass in the fiber is measured to be 28±0.5 rad·(T·m)-1, diverging by less than 3% from the Verdet constant found on the same glass composition in bulk form. These results demonstrate the feasibility to develop reliable tellurite glass fibers by the preform drawing method for magneto-optical applications.     

Two-dimensional finite-difference time-domain simulation for rewritable optical disk surface structure design

A novel two-dimensional finite-difference time-domain simulation for treating the interaction of a focused beam with a rewritable optical disk is detailed and experimentally validated. In this simulation, the real material properties of the rewritable multilayer stack and the aperiodic nature of the disk topography are considered. Excellent agreement is obtained between calculated and measured push-pull tracking servosignals for magneto-optical disks with pregrooves and infinite-length preformat pits. To demonstrate the utility of the simulation as a design tool, the design process for a 0.9-μm track pitch, continuous, composite servoformat magneto-optical disk is given.     

Curie temperature and phase stability of MnBi films exposed to laser pulses of variable duration

Thermomagnetic writing on low-temperature phase MnBi films was investigated. By applying short laser pulses, the undesirable transformation to the quenched high-temperature phase is inhibited. The low-temperature phase proved to be stable when heated for magnetic switching with pulses shorter than 10 μs. The transient temperature during laser heating of a 20 μm diameter film spot was determined using a thin germanium film as a reference target. The temperature shift of the transmission spectrum (λ = 633 nm) of this semiconductor material serves for optical temperature indication. The threshold temperature for stable short-pulse thermomagnetic writing on MnBi was determined by this technique to be 550°C ± 25%. The decomposition temperature was determined to be 820°C ± 25%.     

Magneto-optical non-reciprocal devices in silicon photonics

Silicon waveguide optical non-reciprocal devices based on the magneto-optical effect are reviewed. The non-reciprocal phase shift caused by the first-order magneto-optical effect is effective in realizing optical non-reciprocal devices in silicon waveguide platforms. In a silicon-on-insulator waveguide, the low refractive index of the buried oxide layer enhances the magneto-optical phase shift, which reduces the device footprints. A surface activated direct bonding technique was developed to integrate a magneto-optical garnet crystal on the silicon waveguides. A silicon waveguide optical isolator based on the magneto-optical phase shift was demonstrated with an optical isolation of 30 dB and insertion loss of 13 dB at a wavelength of 1548 nm. Furthermore, a four port optical circulator was demonstrated with maximum isolations of 15.3 and 9.3 dB in cross and bar ports, respectively, at a wavelength of 1531 nm.     

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.     

Optical properties and quantum efficiency of thin-film alkali halides in the far ultraviolet

The optical constants of thin films of CsI, KI, and KBr and the quantum efficiency (QE) of planar photocathodes made with these alkali halides in the 53.6-174.4-nm spectral range are presented. The optical constants were obtained from measurements of the reflectance as a function of incidence angle. The effect of film heating and exposure to UV irradiation on the optical properties and on the QE of the three alkali halides was investigated. KBr was found to be the most stable material for both heating and UV irradiation. KI appeared to be close to temperature stable, whereas UV exposure affected its optical constants. CsI optical constants changed after 420 K heating and after UV exposure. The changes in the optical constants were related to the QE changes, and a certain correlation between both variations was determined. However, it was also demonstrated that the QE changes cannot be explained solely by the changes in optical constants.     

Sources of noise in erasable optical disk data storage

Noise sources in the readback signal for phase-change and magneto-optical disks at red, green, and blue wavelengths are examined, and a simple model is presented to explain the observed noise spectra. For phase-change disks the media noise, which corresponds to ~0.4% fluctuation in the disk's amplitude reflection coefficient, is the limiting performance factor for the conventional detection scheme. In magneto-optical media the depolarization noise, whose fluctuations are ~0.05% of the disk's reflection coefficient, is the major contributor to the media noise in the differential detection scheme. In phase-change optical disks the main sources of noise are the roughness of the groove profiles and the graininess of the polycrystalline recording layer. In nongrooved regions of the disk the media noise measured with green light is found to be nearly the same as that obtained with the red light. In magneto-optical disks the scattering of light from the rough groove profiles, as well as media inhomogeneities, gives rise to depolarization. Measurements on nongrooved regions of a magneto-optical disk indicate that the media noise obtained with the green light is somewhat higher than that obtained with the red light.     

Using the Kramers-Kronig method to determine optical constants and evaluating its suitability as a linear transform for near-normal front-surface reflectance spectra

In this paper, the suitability of using the Kramers-Kronig transform to routinely extract optical constants from near-normal incidence reflectance spectra of solids and liquids is demonstrated. In addition, the possibility of utilizing the Kramers-Kronig transform as a linearizing transform for near-normal incidence reflectance spectra is investigated. Also, several commercial Kramers-Kronig software packages were utilized in determining the optical constants from the near-normal incidence reflectance of Plexiglas. Unexpectedly, the results produced by the various packages differed significantly. The near-normal reflectance of water was measured, the Kramers-Kronig transform was applied to extract the optical constants of water, and the result was compared to values found in the literature. Furthermore, the Kramers-Kronig transforms of near-normal incidence reflectance spectra of various concentrations of sugar in water were calculated to evaluate its use as a linearizing transform for quantitative applications.     

Nonlinear optical, piezoelectric, and acoustic properties of SrB4O7

We have measured the second-order nonlinear optical susceptibilities of an SrB₄O₇ crystal and have determined its electromechanical coupling coefficients, piezoelectric charge and voltage constants, and bulk acoustic wave velocities by a resonance method using high-Q resonators. In addition, the dielectric permittivity of the crystal has been measured at 1 kHz.