The three-dimensional magnetic vector field for a magnetic recording head with unequal pole width is used as an input to a two dimensional extension of the Williams Comstock model to calculate transition charge, erase band widths, and to simulate magnetic force microscope images. Modeling results are compared to MFM images

Signal-to-Noise-Ratio (SNR) is an important indicator of performance in information storage systems. There are many components of noise in magneto-optical (MO) systems. Write noise, the additional noise created by writing on MO media, is an important element the total noise. Recently, several analytical models of write noise [1] were developed based on the assumption that it is caused by the variation in mark edge placement. The edge shift contribution to write noise has two components, an intrinsic media component, and a component caused by the variation in the write laser power. In this paper, power spectral density is used to "e the contribution of write laser power variation to total noise. The power spectrum is used to estimate the write laser power variation.

Analytic models for calculating the contribution to noise power from the writing of periodic patterns of marks in magneto-optical recording are presented. The write noise power distributions are calculated assuming three different models of stochastic variation of the mark edge placement. The standard deviations of the edge placements are estimated from experimental power spectrum.

This paper explores the thermal induced peak shift in magneto-optical (MO) recording. A complete model is presented that includes the writing and reading on magneto-optical media. Data is shown for the readback signal amplitude and peak shift versus write power and pulse length that corroborate the model. The mark shapes are calculated from a purely thermal Green’s function model.

Direct overwrite of thermomagnetically written domains in rare-earth transition-metal thin films using magnetic field modulation has previously been reported. The written magnetization during the low field portion of the field modulation is unsaturated. A new technique for directly measuring the amount of mixed magnetization produced during continuous power laser writing was developed. The field dependence of both the measured amount of mixed magnetization and the measured integrated noise demonstrates a continuously varying mixture of microdomains, plus it yields a direct measure of the saturation field. A comparison to theory using a thermomagnetic write and read simulation was performed. Patterns corresponding to those written experimentally (long, continuous strips) were modeled and characterized. Measures of the mixed states were extracted from the simulation results as a function of applied bias field. From the simulations we computed the average signal, as well as an estimate of the integrated noise power spectrum. These simulation measures of mixed magnetization and its associated noise as sensed in magneto-optic readout have been found to closely match experimental results.

This paper discusses the relationship between optimum laser power and pulse length to obtain the maximum signal amplitude in pulse position modulation magneto-optical (MO) recording. The American National Standards Institute standard (X3B11) for 89-mm disks contains an expression for the maximum allowable optical-pulse power incident at the surface of the recording disk as a function of laser-pulse length: Pw=C[(1/tw)+(1/(tw)1/2], where C=75, Pw is the power in mW, and tw is the laser-pulse duration in nanoseconds. This expression was derived empirically, with C a media characteristic (set to 75 in the standard). To evaluate the adequacy of this empirical equation, disks from five different MO disk suppliers were evaluated for write performance. Having examined different metrics to determine optimum write power for a given laser-pulse length, the power producing the maximum signal amplitude for 1.56-μm mark spacings was selected as the performance criterion. Signal amplitude maximizes because of the competition between mark size and intersymbol interference. The value of the constant in the equation was determined for all media tested. The purpose of this paper is twofold. First, we report the results of our experiments confirming the equation across a broad range of laser powers, pulse lengths, and media types. Second, we modeled the thermal properties of the media and the optical read-back process to explain the empirical relationship among signal amplitude, write power, and pulse length.

A complete model, including both writing and reading, of field-modulated magneto-optical recording is presented. Data are shown to corroborate the model in terms of the readback signal amplitude versus linear density. Mark-edge shapes are calculated from a Green’s function thermal model, and the edges are correlated with the read intensity profile to determine the channel roll-off curve. In addition, the data presented show that the mixed magnetization content in field-modulated recording is not a function of modulation rate. The data reveal the thermal interaction of adjacent marks in beam-modulation recording and the resulting degradation of the channel response relative to field modulation.

A thermal conduction model calibrated with the aid of the measured temperature dependence of the magnetooptic (MO) Kerr effect and MO recording readback data taken with variable reading laser power and disk velocity has been used to provide an estimate of the absolute writing temperature in thermomagnetic recording on MO media. This procedure assumes that such writing is essentially a thermal thresholding phenomenon and that magnetic effects in writing are secondary. The key elements of this method include the following: (a) availability of a flexible thermal model properly calibrated for the MO media under study; (b) measurements of the Kerr rotation of the MO material versus temperature; (c) an accurate experimental method for measuring the differential Kerr readout signal with a dynamic MO disk tester; and (d) experimental data of thermomagnetic writing that is well fitted by a model illustrating the validity of the simple threshold writing temperature concept. The simultaneous regression fitting of a thermal model of MO readback to experimental data results in a fully self-consistent procedure

The classic problem of heat flow in multilayer film structures has been revisited from the perspective of engineering applications for fields such as optical storage media design, laser annealing of semiconductor materials, electron beam lithography, and ion implantation. A compact recursive structure N-layer Green’s function is developed from the coupled partial differential equations of thermal conduction. Temperature profiles are calculated for the absorption of normally incident continuous and pulsed-Gaussian-beam irradiation, on both static and moving media, with variable absorption across the source layer. General beam, amplitude-time dependencies can be calculated with this formalism; however, only simple rectangular pulses are treated in the text. General N-layer solutions are developed, and compact, recursive-integral formulas, whose evaluation is enhanced with modern computer languages such as c and apl, are derived. In addition, we offer a clear physical interpretation of the results expressed by the mathematics, which is a key element that aids successful application of the results to engineering design problems. The physics illuminated by the mathematics suggests a path toward optimal design of the media for enhanced performance, irrespective of the specific application.

The authors explore the thermal behavior of multilayer magnetooptic (MO) storage media in thermomagnetic recording. An attempt has been made to develop a variety of useful models for heat transfer in these disks that can be readily interpreted for ongoing media design activity. Experimental techniques have been devised that can probe the spatial and temporal distribution of the thermal field in the MO storage film. An important feature of these experimental methods is that they use conventional recording hardware for testing recording performance. The experimental work focuses on static, zero-velocity recording experiments in order to clarify the methodology of using thermomagnetic recording process as a high-speed, high-resolution thermometer for the MO film. It is found that each of the models (finite element and method of images) provides an accurate description of experimental measurements of the thermal field in typical MO disk structures.< >

We have measured the low temperature (∼1.8–20 K) heat capacity of the low temperature phases of the silver fast ion conductors AgI, Ag2HgI4, and pyridinium Ag5I6. All three materials displayed non–Debye heat capacities, however, following analysis of the phonon dispersion, no extraordinary behavior or precursory signs of the fast ion transition are seen.

Specific-heat measurements have been made on the mixed-valence tetrathiafulvalene (TTF) salts (TTF)${\mathrm{Br}}_{0.72}$, (TTF)${\mathrm{Cl}}_{0.67}$, and (TTF)${(\mathrm{SCN})}_{0.57}$, at low temperature (2-20 K) and near room temperatures (100-400 K). At low temperatures both positive and negative linear contributions to the specific heat are seen which we attribute to non-Debye phonon spectra. At higher temperatures no specific-heat anomalies are seen at either the metal-insulator or tetragonal-to-monoclinic transitions in (TTF)${(\mathrm{SCN})}_{0.58}$. A broad bump in the specific heat of (TTF)${\mathrm{Cl}}_{0.67}$ at 250 K is attributed to the ordering of the chlorine sublattice. This is the first such observation of an order-disorder transition in these materials. A simple configurational model of this transition is presented.

The low temperature ground state of TTT2I3 with varying amounts of iodide chain disorder has been studied using specific heat and infrared and far infrared reflectance and absorbance. Our results support the model of TTT2I3 as an organic conductor at room temperature which undergoes a metal to insulator transition near 50 K. At low temperatures we find a semiconducting gap of 80 cm−1 independent of disorder.

In an attempt to find any precursor signs of the fast ion state in silver conductors; we have measured the low temperature (1.8–20K) specific heats of AgI, Ag 2 HgI 4 , and Pyridinium Ag 5 I 6 . While all three materials displayed non-Debye specific heats no extraordinary behavior was seen.