Thermomagnetic writing in homogeneous MnBi films

The specific Faraday rotation of the homogeneous low-temperature phase (LTP) and quenched high-temperature phase (HTP) MnBi films used for the writing experiments was measured to be9.5times10^{5}degrees per centimeter and4.3times10^{5}degrees per centimeter, respectively, at 25°C and a light wavelength of 632.8 nm. The coercive field of the films decreased exponentially with increasing film thickness for both phases. Thermomagnetic writing experiments showed that the written spots (1 to 10 μm in diameter) were not satisfactorily stable for films thicker than 50 nm. If thicker films are to be used for magnetooptic memory applications, they should possess larger wall-motion fields than the films investigated, in order to achieve stable spots. The erasure field of the spots was found to depend on the strength of the applied writing field and on the duration and the power of the heating laser pulse. A writing-erasing hysteresis was recorded by means of the Faraday effect. A thermal saturation field is introduced and measured in dependence on film thickness for LTP films. With the help of this field and wall-pinning effects, thermomagnetic writing in MnBi films is discussed.     

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%.     

Media for erasable magnetooptic recording

Amorphous rare-earth-transition-metal alloys are considered as materials for magnetooptic information storage. They can be prepared by evaporation or sputtering on glass or polymer substrates. The alloys are ferrimagnets and exhibit a uniaxial magnetic anisotropy. The magnetic and magnetooptic properties can be well tailored by the composition as well as the deposition conditions. The information is stored by memory magnetic domains which can be written by a thermomagnetic switching process. The reading process utilizes the magnetooptic Kerr effect. In both cases the temperature profile of the saturation magnetization, the uniaxial anisotropy, and in particular the coercivity are of primary importance. At present, the most prominent candidates for device applications are GdTb-FeCo and Tb-FeCo alloys. Carrier-to-noise values up to 61 dB (30 kHz) have been achieved using magnetooptic disks     

A proposed beam-addressable memory

The feasibility of optical beam-operated magnetic storage systems is assessed. Recent advances in laser technology and in transparent magnetic materials are described along with methods for writing and reading information. In the writing process, thermomagnetic recording on thin films is considered and the writing speed and resolution is calculated, illustrating the large performance improvement obtainable compared with existing magnetic recording techniques. The progress in materials, beyond the previously used metals, has developed towards more transparent magnetic media while retaining large intrinsic magneto-optical rotation. Consequently, large signal-to-noise ratios are obtained which relax the material uniformity requirements. The properties of ferrites, garnets, and rare-earth compounds are compared with metals to illustrate this advance. At the present time, technical problems exist with a light beam in achieving random access to a large field. This limitation is alleviated, however, in certain types of memories where the access requirements combine sequential and random motions. As an example, a prototype memory is discussed for a computer input-output system having certain performance advantages. In this memory, sequential access is achieved with a rotating mirror and random access by means of a digital light-deflector.     

Thermomagnetic recording: Physics and materials

Thermomagnetic recording is the production of a remanent magnetization in a material by cooling it from a critical temperature in a small magnetic field. The most prominent applications for thermomagnetic recording presently under consideration are high density information storage and tape copying; other applications, e.g., display and magnetic printing, can also be envisioned. In this review of the field, we discuss the proposed applications of thermomagnetic recording, the physical principles of the various magnetic phenomena that can be used for this purpose, and the degree to which specific materials meet the requirements for thermomagnetic recording.     

Optical,magneto-optical and structural properties of Mn,Bi and MnBi in the form of thin films

The optical and magneto-optical constants of MnBi were measured because of its potential as a medium for magneto-optical information processing. In addition, the optical constants of Mn and Bi were also measured since a knowledge of these constants can be useful for optically monitoring the formation process of MnBi. Thus it is desirable that values of the constants of MnBi and its constituents are reliable. An assessment is therefore given of the reliability of the constants in the literature based on the structural investigations of thin films of these materials.     

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.     

Experimental evaluation of an MnBi optical memory system

An experimental optical memory system is described for evaluating the optical memory characteristics of MnBi films. The preparation procedure for obtaining large uniform films is discussed. These films require about 10 mW of laser power to write 1-μm bits and a coincident field of 600 Oe to erase them. A packing density of 1.5 × 10⁸bit/in²with a typical signal-to-noise ratio of 10 is readily achieved. Large area films have been sample tested and found to be of usable quality over 99.9 percent of the area. Test bits have been repeatedly cycled to the Curie point more than 10⁶times retaining an adequate signal-to-noise ratio.     

Linear and non-linear optical and spectroscopic properties of Langmuir-Blodgett films

Optical and spectroscopic properties of Langmuir-Blodgett (LB) monolayers and multilayers are being measured to characterize the films, to understand their two-dimensional behavior and to follow chemical and physical changes. Orientation of groups and molecular packing have been analyzed by Fourier transform IR spectroscopy at glancing angle, from waveguide Raman scattering and from near- edge X-ray fine structure. Use in electronic and optical devices has excited many, especially with non-linear phenomena needed to control or modify light optically for communication and storage. Recent optical results on thin monolayer and multilayer assemblies will be reviewed, including both the linear and non-linear aspects. Effects and phenomena will be illustrated with examples to give an appreciation for their use and to display some of our new knowledge about LB films.     

Ferrimagnetic garnet films for magnetooptic information storage

Reversible magnetooptic memories are believed to compete favorably with magnetic bubble devices and CCD's if economic low-power light sources can be used. For optical information storage at data rates of >10⁶bit/s and blocks of 10³bit, memory materials are required exhibiting an optical recording sensitivity on the order of the photographic plate. The presented contribution outlines the recently proposed concept of a magnetooptic/photoconductive sandwich, called MOPS, and shows that certain ferrimagnetic garnet compositions can especially be adapted to such applications.     

Novel multifunctional nanocomposites from titanate nanosheets and semiconductor quantum dots

A novel synthesis for a titanate nanosheets loaded nanocomposite has been developed. On this basis, a multifunctional material for optical applications has been fabricated with tunable refractive index, improved processing behavior and luminescent properties imparted by the incorporation of semiconductor quantum dots.Titanate synthesis, host material choice and quantum dots functionalization have been here addressed to obtain films with good optical quality and stable photoluminescence.In order to assess the potential application of the obtained nanocomposites, imprinting lithography and aerosol-based deposition techniques have been applied with promising results.The obtained nanocomposites have been characterized by UV–Vis, photoluminescence and FT-IR spectroscopy, X-ray diffraction and Transmission Electron Microscopy. The optical properties of the nanocomposite film have been tested by spectroscopic ellipsometry and M-line technique.     

Kerr effect imaging of dynamic processes in magnetic recordingheads

Techniques for imaging microscopic dynamic magnetic phenomena in magnetic recording heads are reviewed. Two experimental apparatus which utilize the Kerr magnetooptic effect are described. A scanning magnetooptic photometer uses the principles of confocal optical microscopy in which a focused laser spot serves as a high-resolution (~0.3 μm) probe of magnetic activity to very high frequencies (250 MHz). Magnetooptic flash photography uses the technique of stroboscopic imaging with digital image processing to provide instantaneous (10 ns exposure time) images of magnetic phenomena on a microscopic scale by utilizing a pulse laser for illumination. Results from various studies of ferrite, metal-in-gap, and thin-film magnetic recording heads using these apparatus are reviewed along with their methods     

Structural and optical properties of electron beam evaporated CdSe thin films

Thin films of cadmium selenide (CdSe) as a semiconductor is well suited for opto-electronic applications such as photo detection or solar energy conversion, due to its optical and electrical properties, as well as its good chemical and mechanical stability. In order to explore the possibility of using this in optoelectronics, a preliminary and thorough study of optical and structural properties of the host material is an important step. Based on the above view, the structural and optical properties of CdSe films have been studied thoroughly in the present work. The host material, CdSe film, has been prepared by the physical vapour deposition method of electron beam evaporation (PVD: EBE) technique under a pressure of 5 × 10⁻⁵ mbar. The structural properties have been studied by XRD technique. The hexagonal structure with a preferred orientation along the (0 0 2) direction of films has been confirmed by the X-ray diffraction analysis. The films have been analysed for optical band gap and absorbed a direct intrinsic band gap of 1·92 eV.     

Magnetooptics, lasers, and memory systems

The field of magnetooptics is reviewed and the application of a magnetic memory system as a readout technique is discussed. A review and comparison of the fundamental magneto-optic effects and their utility in a system is presented. It is shown for a longitudinal Kerr readout system that laser and shot noise limit wide-band (1 MHz) signal-to-noise ratios to about 40 dB. Media noise problems are reviewed. The limitations to packing density are discussed, and it is concluded that packing densities greater than 10⁷bit/in²(including suitable guardbands) are practical. The various techniques for optico-thermal recording are surveyed. A discussion of related hardware components (such as optical modulators and lasers) is presented. It is concluded that a viable magnetooptic detection-laser beam memory system is practical. No suitable nonmechanical scanning system has yet been developed.     

应用于DRAMs的钛酸锶钡薄膜的研究进展

随着DRAMs存储密度的增加,传统材料已不再适用于将来的DRAMs技术的发展.在目前研究的新型替代材料中,钛酸锶钡以其优越的介电性能越来越引起人们的关注.介绍了随DRAMs的发展趋势,钛酸锶钡薄膜的研究进展,包括其制备方法、研究状况及影响其介电性能的因素,并提出了下一步研究工作中需要解决的几个问题.     

The stability of EuO films doped with iron and europium

The feasibility of a low-temperature beam-addressable memory utilizing EuO films doped with iron and excess europium as the storage medium is dependent upon the chemical stability of the divalent state of europium. The stability of such EuO films covered with a protective layer of Eu2O3has been examined as a function of temperature in various oxidizing atmospheres. The degradation of the films was monitored by measuring optical absorption and transmission, Faraday rotation, coercive force, hysteresis loop squareness, Curie temperature, and lattice constant as the films were progressively aged. The results show that these protected EuO films are stable even in oxidizing atmospheres and at high temperatures relative to the operating temperatures which would be required for a beam-addressable file based on this material.     

On the optical and electrical properties of rf and a.c. plasma polymerized aniline thin films

Polyaniline is a widely studied conducting polymer and is a useful material in its bulk and thin film form for many applications, because of its excellent optical and electrical properties. Pristine and iodine doped polyaniline thin films were prepared by a.c. and rf plasma polymerization techniques separately for the comparison of their optical and electrical properties. Doping of iodine was effectedin situ. The structural properties of these films were evaluated by FTIR spectroscopy and the optical band gap was estimated from UV-vis-NIR measurements. Comparative studies on the structural, optical and electrical properties of a.c. and rf polymerization are presented here. It has been found that the optical band gap of the polyaniline thin films prepared by rf and a.c. plasma polymerization techniques differ considerably and the band gap is further reduced byin situ doping of iodine. The electrical conductivity measurements on these films show a higher value of electrical conductivity in the case of rf plasma polymerized thin films when compared to the a.c. plasma polymerized films. Also, it is found that the iodine doping enhanced conductivity of the polymer thin films considerably. The results are compared and correlated and have been explained with respect to the different structures adopted under these two preparation techniques.     

Deposition by magnetron sputtering and characterization of indium tin oxide thin films

In this work the properties of indium tin oxide (ITO) films deposed on glass substrates by magnetron sputtering technique in the temperature range below 200 °C are studied by various methods. The physical properties of ITO thin films have been investigated using optical transmittance, photoluminescence, atomic force microscopy, ellipsometry, Hall-effect and four point probe methods. It is established that properties of ITO layers depend drastically on the temperature and oxygen partial pressure during the deposition process and exhibit some peculiarities of the surface morphology. It is found that the band gap energy of this material varies in the energy range from 4.1 to 4.4 eV and depends on the growth conditions. It is suggested that local deviations from the stoichiometry and defects are the main physical reasons of Burstein-Moss shift of the optical band gap.     

A CRITICAL REVIEW OF LASER ABLATION-SYNTHESIS OF HIGH TEMPERATURE SUPERCONDUCTING FILMS

Laser ablation-deposition has become one of the most widely used techniques for synthesizing high temperature superconducting thin films. Therefore, it is important to understand the basic phenomena involved in laser-solid target interaction, and ablation, transport, and deposition of material onto appropriate substrates. Basic phenomena related to these processes are discussed in view of recent experimental and theoretical work performed by several groups, with the ultimate goal of optimizing this deposition technique and scaling up for application in technologies such as microelectronics     

Effect of relative humidity on the optical and waveguide properties of thin chitosan films

We have measured the optical characteristics of thin films based on various ion forms of chitosan and studied their mutual correlation. Using the spectral ellipsometry and mode spectroscopy techniques, it has been established that the optical characteristics of chitosan depend on the relative humidity (RH) of the ambient medium. All samples are characterized by threshold RH values, at which the optical characteristics exhibit a change. The obtained data allow chitosan to be classified as a promising sensor material with the optical properties controlled by relative humidity of the ambient medium.