Study of Lithographically Defined Data Track and Servo Patterns

We report on fabrication of discrete tracks on perpendicular magnetic recording (PMR) media with an e-beam lithographical process. We studied the recording performance of the e-beam media on a spinstand in parallel with conventional PMR media. Discrete track media show significant reduction in adjacent track erasure (ATE). We studied and quantitatively measured the source of the ATE improvement, and developed a triple track geometrical model to calculate achievable track density for both discrete track recording (DTR) and continuous media. From the model, we identify two factors of DTR that contribute to reaching a higher TPI. Using the same fabrication technique, we also studied servo burst design and its playback waveform quality. At 250 ktpi, we compare DTR servo bursts with servo bursts written with a conventional method. DTR servo bursts show better edge definition, which can translate to better position error signal sensitivity and support higher TPI in the future.Discrete tracks are fabricated on conventional PMR media with an e-beam litho graphical process. The recording performance is studied on a spinstand in parallel with conventional PMR media. Discrete track media shows significant reduction in adjacent track erasure (ATE). The source of the ATE improvement is studied and quantitatively measured. A triple track geometrical model is developed to calculate achievable track density for both DTR and continuous media. From the model, we identify two factors of DTR, which contribute to reaching a higher TPI. Using the same fabrication technique, we also study servo burst design and its playback waveform quality. At 250 ktpi, we compare DTR servo bursts and servo bursts written with a conventional method. DTR servo bursts show better edge definition, which can translate to better PES signal sensitivity and support higher TPI in the future.     

Fe2O3的掺杂对TSSG法生长Zn:Fe:LiNbO3 晶体的结构和光折变性能的影响

本文利用TSSG方法生长了不同掺Fe2O3浓度的Zn∶Fe∶LiNbO3晶体,并对晶体进行了红外光谱、紫外光谱、晶格常数和居里温度的测试和分析.利用二波耦合实验测得的写入和擦除曲线,计算了晶体的写入时间常数、擦除时间常数和最大衍射效率.并讨论了Fe2O3的掺杂对材料结构和光折变性能的影响机制.     

Erase profiles of floppy disk heads

An experimental method is described to measure the amplitude profiles across written tracks used in rigid and floppy disk drives. This method allows determination not only of read, write, and side-erasure widths associated with the heads, but also of the detailed shape of the written profiles. These profiles may be obtained for tracks in the as-written condition, or after modification by the write or erase functions of the head. This method was applied to floppy disk heads in order to determine the trim erase characteristics of straddle erase, tunnel erase, and the implicit side erase characteristic of the read/write core itself. A number of typical track profiles are shown, demonstrating the usefulness of this technique. It was found that the straddle erase elements exhibit erasure both under the air gap and under the poles straddling the read/write core; the tunnel erase elements exhibit uniform erasure across their erase gaps but are subject to azimuthal misalignment effects; and the read/write cores themselves exhibit an implicit erase function during normal writing which, in the case studied, extended about 360 μm (9 μm) to each side of the core. Applications of this method to evaluate heads for use at high track densities are also outlined.     

Side fringing fields and write and read crosstalk of narrow magnetic recording heads

In magnetic recording systems the side fringing fields of magnetic recording heads are responsible for crosstalk from adjacent tracks and eventually for partial erasure of adjacent tracks, thereby limiting the attainable track density. In this paper we derive analytical expressions for the magnetic field near the side of a recording head and calculate the cosine transform of the longitudinal field component, with the head side angle and gap length as parameters. The field of a head of zero width is also considered. Due to the side fringing field the written track is somewhat wider than the geometrical head width; the increase in width being approximately proportional to the maximum field strength in the recording medium and the head-to-medium distance. The amplitudeuof the read crosstalk signal from an adjacent, infinitesimally narrow track is calculated and it appears that it can be approximated byu/u_{0} = 0.5 exp (-2pi x/lambda), where u0is the on-track signal (with zero head-to-medium spacing),xis the distance between track and head side, and λ is the wavelength. Maximum track densities are calculated for a specified crosstalk-to-signal ratio and a given head width and wavelength. For a wavelength of 10 μm, a head width of 5 μm, and a crosstalk of -20 dB, the track density is limited to about 130 tracks/mm, assuming a track width equal to the head width. When the track is taken to be 5 μm wider than the head to account for the effects of the write process, no guardband at all is needed for -20 dB crosstalk and the limit to the track density is 100 tracks/mn.     

Photorefractive trapping and the correlation between recording and erasure dynamics in a polymer composite

Abstract

The fast time constants of holographic contrast growth and erasure for various photorefractive polymer composites were measured under a wide range of experimental conditions. Either of two sensitizers, 2,4,7-trinitro-9-fluorenone (TNF) or (2,4,7-trinitro-9-fluorenylidene)malonodinitrile (TNFDM), were used in a degenerate four-wave mixing experiment under varying conditions of field, wavelength and intensity. Collected together, the fast growth and erasure time constants were found to be correlated with a coefficient of 0.96. From this correlation we conclude that the charge generation process during holographic recording and the optical de-trapping process during hologram erasure are indistinguishable. Hence in accordance with the photorefractive crystal model, hole recombination with the sensitizer anions forms the primary charge trapping mechanism in the majority of photorefractive polymer composites.     

Longitudinal recording in a stray field

We have studied the sensitivity of soft error rate (SER) to an external magnetic field in longitudinal hard disk drives. We found that during writing SER is generally quadratic with field amplitude and symmetric with field direction. The application of an external field during writing also shifts the center of the track. In contrast, during reading SER is predominantly linear with field amplitude and antisymmetric with field direction. There is no shift in the track center when the field is applied during reading up to 100 Oe. We explain the difference in the track center shift between writing and reading in terms of the effect of the stray field on the servo positioning system.     

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.     

Exciton Self–Trapping and Lattice Defect Creation in Rare Gas Solids and Other Insulators

We have studied the possible creation of stable lattice defects induced by exciton self–trapping (STE) in solid neon. Generally speaking, the STE–bubbles accompanied with a plastic deformation are found to be at lower energies than a pure STE–bubble. Those with two vacancies in the first atomic shell have the lowest energy. Some of the vacancy–interstitial atom pairs escaped mutual annihilation as the electronic sub–system returned to the ground state, thereby stable lattice defects resulted. The emission energy changes of lattice defect–associated STE have been evaluated and are found to be in reasonable agreement with observed data. Much has been learned recently on the role of the STE in radiation damage creation of ionic halides. We have made a brief comparison of the ionization induced defect formation processes in the two types of materials. In both cases, the excited electron is the prime driver of the process. In solid neon the excited electron is directly attracted to the localized hole on Ne, but repelled by the ground state Ne atoms. In the halides the excited electron is attracted to the Madelung potential at an anion site instead. In rare gas solids, the Frenkel pair is a purely structural defect in the lattice with the electronic subsystem in its ground state. In ionic halides, the pair of F center and H center is not only an interstitial atom–vacancy pair in the halogen sublattice, but also represents an electronically excited state. Because of this difference the way the created Frenkel defects are stabilized in the two types of material is distinct.     

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.     

Spin-current-driven thermoelectric coating

Energy harvesting technologies, which generate electricity from environmental energy, have been attracting great interest because of their potential to power ubiquitously deployed sensor networks and mobile electronics. Of these technologies, thermoelectric (TE) conversion is a particularly promising candidate, because it can directly generate electricity from the thermal energy that is available in various places. Here we show a novel TE concept based on the spin Seebeck effect, called 'spin-thermoelectric (STE) coating', which is characterized by a simple film structure, convenient scaling capability, and easy fabrication. The STE coating, with a 60-nm-thick bismuth-substituted yttrium iron garnet (Bi:YIG) film, is applied by means of a highly efficient process on a non-magnetic substrate. Notably, spin-current-driven TE conversion is successfully demonstrated under a temperature gradient perpendicular to such an ultrathin STE-coating layer (amounting to only 0.01% of the total sample thickness). We also show that the STE coating is applicable even on glass surfaces with amorphous structures. Such a versatile implementation of the TE function may pave the way for novel applications making full use of omnipresent heat.     

Combatting partial erasure and transition jitter in magneticrecording

Practical recording channels deviate significantly from the oft-used model based on linearity and additive Gaussian noise. Among the well-known anomalies are partial erasure and transition jitter. In this paper, we first describe a precompensation technique to combat the partial erasure effect. It utilizes the unique property of the maximum transition run (MTR) code wherein all dibits are isolated. The idea is to increase the spacing between the two transitions that make up each dibit. This tends to mitigate the nonlinear amplitude reduction associated with partial erasure. Next, we consider a recording channel that is linear but subject to transition jitter. We modify the hyperplane-based detector known as 3D-110 by introducing data-dependent threshold terms. The overall complexity of the detector is small, yet this modification provides almost 2 dB of improvement relative to the original 3D-110 structure and the extended partial response maximum likelihood (EPRML) method tuned to additive Gaussian noise     

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.     

The dependence of direct overwrite characteristics on the magnetic properties of DC magnetron sputtered films

The magnetization of rare-earth transition metal films was varied by changing the compensation and the Curie temperatures independently. The coercivity was varied by depositing films with different thicknesses and with an underlayer of silicon nitride. The direct overwrite characteristics investigated include the minimum pulsewidth for erasing and writing a certain size domain, the pulsewidth margins for erase, and the erasable size of domain. The minimum pulsewidth for erasing domains increases when the film thickness increases or an underlayer of silicon nitride is deposited between the magnetic layer and its glass substrate. The poorer erasure performance is due presumably to the higher coercivity at high temperatures in the thinner films. A decrease in the compensation temperature leads to an increase in the magnetization of high temperatures and causes the minimum erasure pulsewidth to increase and the largest erasable domain size to decrease.<>     

Photorefractive gratings in DR1-doped hybrid sol–gel films

Photorefractive gratings have been obtained with 632.8 nm writing beams in organic–inorganic SiO₂-based films. The hybrid glass is prepared by a sol–gel technique, starting from organic Si precursors, and contains Disperse Red 1 (DR1), carbazole units and 2,4,7-trinitro-9-fluorenone (TNF). The photorefractive gain, which has been found unexpectedly even without poling field, has been determined through an asymmetric energy exchange by two-beam coupling measurements. The effects of the polarization of the writing beams and of a circularly polarized photoisomerizing radiation during the erasure of the grating have been interpreted in terms of an orientational contribution to the grating formation.     

Interpolation of erasure bursts via cosine-modulated filterbanks

A novel and low-complexity approach for reconstructing periodic erasure bursts in data sampled at greater than the Nyquist rate, using cosine modulated filterbanks, is described. In the case of interpolation of erasure singlets or doublets periodically repeated over 2M samples, the cosine modulated filterbank approach is shown to have a lower complexity (for a given restoration error) than a standard FIR interpolator. In the case of erasure triplets or quadruplets, periodically repeated over 2M samples, the restoration error is primarily related to whether theM-channel filterbank’s stopband suppression is better than the condition number of a 2 × 2 matrix, whereM is determined by the oversampling factor of the data. While the method used for erasure triplets and quadruplets extends to arbitrary erasure bursts, the condition numbers of the associated (larger dimension) matrices deteriorate rapidly with the increase in erasure length, posing practical problems such as the design of very high-attenuation filterbanks and large required implementation wordlengths.     

Adjustable balancer with electromagnetic release of balancing members

Adjustable balancers are useful in applications where rotational imbalance is frequently varied. For example, in media level servo track writers used in the hard disk drive industry, a set of blank disks is loaded on a spindle motor for the purpose of servo writing. Since servo writing is performed at high speeds, imbalance introduced by disks and spacers results in significant vibrations that can affect the quality of the servo writing process. This paper proposes a new configuration of adjustable balancer that enables to compensate for rotational imbalance each time a new set of blank disks is loaded into the servo track writing machine. The adjustable balancer is ring shaped with a number of grooves displaced around axis of rotation. Steel balls are placed inside the grooves and held by permanent magnets. Imbalance compensation is achieved by electromagnetically activated release of the steel balls. The main advantage of the proposed configuration is its large compensation range. Presented three-dimensional finite-element analysis results and experimental results demonstrate and prove the effectiveness of this novel configuration.     

A Fast and Accurate Method for Measuring Adjacent-Track Erasure

This paper reports on a novel spin-stand method to measure adjacent-track erasure (ATE). The method divides a track into multiple sectors and makes use of the built-in servo system to ensure a highly accurate, amplitude-based measurement. By arranging subtracks uniformly across the range of interest around a center track, a quasi-continuous, detailed ATE profile can be obtained. We discuss the various features of this profile and how they depend on such parameters as skew angle, write current, frequency, and flying height. We then compare the ATE performance of state-of-the-art longitudinal and perpendicular recording components under realistic test conditions, such as may be used for a 250 GB/platter 95 mm desktop drive. We show that the perpendicular head and media compare favorably to longitudinal ones even though the track width is much narrower     

Experiments on high excitation density, quenching, and radiative kinetics in CsI:Tl scintillator

Information on quenching as a function of electron-hole density through the range of 10¹⁹ to 2×10²⁰ e-h/cm³ typically deposited towards the end of an electron track has been acquired using 0.5 ps pulses of 5.9 eV light to excite in the band-to-band or high-exciton region of CsI and CsI:Tl. A streak camera records partially quenched luminescence from self-trapped excitons (STE) and excited activators (Tl^+?). Both the Tl^+? and STE luminescence exhibit decreasing light yield versus excitation density N_max, but it is only the 302 nm STE luminescence that exhibits decay time quenching dependent on N_max. Fitting the STE decay time data to a model of dipole-dipole quenching yields the time-dependent bimolecular rate constant for quenching of STEs (and Tl^+? light yield) in CsI at room temperature: k₂(t)=2.4×10⁻¹⁵ cm³ s^−1/2 (t^−1/2).     

Digital quasi-phase-matched two-color nonvolatile holographic storage

Unwanted erasure during readout of holographic data can be reduced or eliminated by use of a different wavelength for reading than that which was used for writing. To prevent distortion and Bragg mismatch that would be unacceptable for digital data storage, one can format data to account for the wavelength difference. Techniques to format data and the results of this formatting are presented. Varying the formatting parameters is investigated to optimize diffraction efficiency.     

Thermally activated electrostatic injection of solvated ions by a track membrane interfaced vacuum feedthrough

Electromembrane ion sources are considered as potential techniques for direct mass spectrometric sampling from ambient conditions. Interfacing of a time-of-flight mass spectrometer by means of a poly(ethylene terephthalate) track membrane requires investigation of the thermally activated processes involved. In this study, we directly attempt substantiating an activation-like performance of such track membrane-mediated interfaces. A number of KCl/glycerol solution samples were tested. A wide range of fixed, externally applied, potential drops was covered. For the charge extraction processes studied, we observe and discuss an activation term, exp(-ΔF/k(B)T), with a free-energy barrier ΔF = ΔF(0) - ΔF(Φ). The potential drop-dependent ΔF(Φ), was found to be sensitive to the varying salt concentration.