Write Field Gradient Research Articles

Theoretical study of nonlinear transition shift in double-layer perpendicular media

Nonlinear transition shift (NLTS) in perpendicular media is studied theoretically. From an analytic expression for demagnetizing field in perpendicular media, the difference between transition shift and NLTS is shown. A finite-element model is used to study the influence of a high permeability write head on the demagnetizing field from the adjacent transition. The results show a negligible effect, unlike longitudinal recording. Using a write model, the relationship between NLTS and write field gradient of perpendicular media shows that NLTS approaches a constant as the gradient increases. We also demonstrate that the measurement of the undifferentiated signal (the direct readback signal from perpendicular media) using the harmonic elimination technique produces misleading results.

Simulation of servo position error signal in perpendicular recording

We describe simulations using a medium model with random grain structure, to study the servo position error signal (PES) in a perpendicular recording system. Under various detection schemes, values of the PES null position jitter and the PES sensitivity variation at the null point are calculated. To evaluate the effect of medium noise on the PES detection, the values are compared to those of media with different average grain in-plane areas and grain size distributions. For both the PES null position jitter and the PES sensitivity variation at the null point, decreasing the average grain in-plane area or the grain size distribution yields smaller fluctuation. The servo PES has a strong dependence on the average-medium grain in-plane area. When PES of longitudinal recording systems is compared with that of perpendicular systems, perpendicular recording yields much better results because of a sharp write-field gradient at the track edge.

Analytical model for estimation of isolated transition width in perpendicular magnetic recording

In order to discuss the relationship between the magnetic properties of recording media and the isolated transition widths, an analytical model for the calculation of transition parameters is proposed. In the model, Lorentzian distributions of coercive forces of the magnetic particles in the media are assumed, with half peak widths and mean values corresponding to the coercive forces of media measured in the direction perpendicular to the medium surface. The magnetization distribution after writing an isolated transition can be obtained self-consistently as an arctangent function, in which the writing field gradient of a head, the particle coercive force dispersion of the medium, the demagnetizing field and the interparticle exchange interaction are taken into account.

Spin stand study of density dependence of switching proprieties in patterned media

The recording processes of patterned bits with different bit length generated by focused ion beam etching are investigated by spin stand testing. Compared to conventional written transitions, the magnetization switching of patterned bits requires much smaller write fields. Also the write field gradient is no longer critical to the sharpness of the transition of patterned bits. Experimental results demonstrate that from the standpoint of recording, patterned media is a good solution for ultra-high density magnetic recording.

Write bubble and field rise time measurements

An experimental technique has been developed for studying the write bubble created by the thin film recording heads. From the measurements of the write bubble size, we can estimate the write field magnitude and the write field gradient at the write bubble boundaries. Using the same experimental setup, we can also study the write field high frequency characteristics.

Williams-Comstock model with finite-length transition functions

The theory of the third-order-polynomial (TOP) and fifth-order-polynomial (FOP) magnetization transitions is presented. These transitions have a finite length, rather than an asymptotic approach to /spl plusmn/M/sub r/., which is the case with some widely-used transition functions. The Williams-Comstock model is used to obtain the transition parameters, which are equal to half the transition lengths, resulting in quadratic equations and simple expressions. In this analysis, the write-field gradient is maximized with respect to the deep-gap field, as well as with respect to the distance of the transition from gap center, which results in a higher gradient than is obtained with the original Williams-Comstock approach, at the expense of a higher write current. Analytic expressions are obtained for the read pulses of inductive and shielded magnetoresistive heads, and equations for nonlinear transition shift are derived for the arctangent and the TOP transitions. The results are compared with those obtained using arctangent and tanh transitions and with experiment. In addition, certain aspects of the write-process Q function and the optimum deep-gap field are discussed.

Effective field gradient dependence on write field rise time

An analytic expression has been obtained for the field gradient of a recording head at the moment that the write process is completed. Although the head gap is assumed to be much less than the fly height, expressions for the effective spacing of wide gap heads extend the results. From this analysis, it is found that the maximum normalized write field gradient can be obtained, by increasing the write field strength, to partially compensate for poor rise time.

Temperature effects in barium ferrite particles

Barium ferrite particulate media have attracted considerable interest for high density magnetic recording applications because they can be oriented to provide a perpendicular easy axis of magnetization and they can be mass-produced with existing coating facilities. Their perpendicular magnetization endows them with excellent short wavelenght response, but at the same time tends to highlight writing field deficiencies, because the perpendicular component of the writing head field is considerably smaller than the horizontal head field component. The situation is further aggravated by the employment of very narrow gap ring heads, dictated by the need to provide a sharp writing field gradient and to avoid read gap losses. When you consider these potential limitations, the first casualty we are likely to encounter is overwrite performance, particularly in interchangeable media applications. If, in addition to the above, we also have some temperature variation of the magnetic parameters, then temperature dependence of overwrite modulation could become unacceptable. In this study, we measured the temperature coefficients of the magnetic parameters of many different Ba-ferrite particles and coatings. We found very large differences among the various particles which can be explained on the basis of a simple theoretical model. We conclude that it is necessary and possible to make a Judicious choice of particle characteristics in order to avoid any potential temperature-related problems in recording applications.

Fourier synthesis of digital recording waveforms

A digital recording system is modeled by means of a complex Fourier series representation employing transforms of arctangent functions to describe the effects of write field gradient demagnetization and self-demagnetization. Pulse asymmetry and rise time effects are incorporated by means of phase shifts from complex transfer functions used in describing the dependence of head properties on a complex permeability. Experimental measurements on a specific system (Co substituted γ-Fe 2 O 3 tape and metal heads) show good correlation with the theory, especially with respect to spectral content, waveform shape, and peak shifts. The model is one-dimensional and limited to recording media initially ac demagnetized and to a write current range in which it is possible to define an effective penetration depth for saturation recording.