Thin-film Longitudinal Recording Media Research Articles

Magnetization estimation from MFM images

We have developed a method to estimate the complete magnetization in thin-film longitudinal recording media from magnetic force microscopy (MFM) data. The method uses a medium model described by a Voronoi tessellation of the film plane. The magnetization lies in that plane, has constant magnitude, and is uniform within each convex region, or grain, of the tessellation. The effect of a single grain on the MFM simulation is isolated by considering the difference between the MFM images before and after that grain undergoes a 180/spl deg/ magnetization reversal. Using this difference image, the complete magnetization of the grain and the grain's boundaries are estimated. By isolating each grain in turn, as if a series of incremental applied fields had been applied, the magnetization for the whole pattern is estimated.

Microstructural and crystallographic aspects of thin film recording media

Various aspects of the structure of thin film longitudinal recording media are presented and discussed. In particular we discuss the role that the various layers of thin film media play in controlling the microstructure and magnetic properties of the magnetic layer. These include the grain size of the films, the texture of the films, the role of the intermediate layer and the role of chemical segregation.

The Development and Characterization of Crystallographic Texture in thin films for Magnetic Recording

ABSTRACTThe development of crystallographic texture in thin film longitudinal recording media is discussed. Polycrystalline thin films may obtain their crystallographic texture by means of a nucleation process such as epitaxial nucleation on a polycrystalline underlayer or by means of a process involving a preferred growth direction. In this paper we will discuss various epitaxial nucleation textures that are obtained in media produced for magnetic recording. We will discuss the way that the underlayer controls the crystallographic texture of the magnetic layer, as well as methods used to control the texture of the underlayer itself. We give a brief overview of some of our recent findings in the growth of NiAl and FeAl films used for underlayers. Finally we will briefly discuss what we have called the tilted electron beam technique. In this technique selected area electron diffraction patterns are obtained at different angles of tilt and the development of arcs in the patterns is analyzed so as to determine the type and amount of crystallographic texture which is present in the films.

Overwrite Modulation in Co-Based Thin Film Longitudinal Recording Media

Two mechanisms of overwrite, incomplete erasure and modulation, have been studied quantitatively for Co-based thin film longitudinal recording media with a variety of media parameters using thin film head. For all the media studied, the modulation component is larger than the incomplete erasure component under sufficient write current condition. As MrT or the head-medium spacing increases, the incomplete erasure component does not change, instead, overwrite degrades because of the increase in the modulation component. The increase in Hc affects overwrite performance through the increase in both incomplete erasure and modulation component. The relationship between overwrite and media noise performance is also discussed from the view point of media microstructure.

Coercivity angular dependence in longitudinal thin film media

Computer simulation study of coercivity out-of-plane angular dependence in thin film longitudinal recording media combined with experimental measurements is presented. A theoretical model developed for studying micromagnetic processes in polycrystalline thin films was utilized for the calculations. Films with crystalline easy axes of the grains randomly oriented in three dimensions as well as in the film plane are investigated. The coercivity angular dependence is analyzed by varying magnetostatic and intergranular exchange interactions broad ranges. The coercivity angular dependence is characterized by two quantities: the angular position of the coercivity maximum and the normalized difference between the maximum coercivity and in-plane coercivity. The former quantity exhibits significantly different behavior with separately varying the magnetostatic interaction strength and intergranular exchange coupling. The difference may allow us to distinguish the two types of interactions and it may allow us to determine the crystalline anisotropy constant and an effective intergranular exchange coupling strength in the film simultaneously from experimental measurements. Specifically designed experiments are carried out to verify the theoretical calculations. Reasonable agreements between the calculations and experimental measurements are obtained.

Noise of interacting transitions in thin film recording media

The noise of interacting di-bit transition pairs in thin-film longitudinal recording media is studied via computer simulations. It is shown that the intergranular exchange coupling yields large-scale irregular transition boundaries, and thereby large transition noise. At small bit intervals, the magnetostatic interaction field that has resulted from such a noisy transition significantly enhances the noise of a later adjacent transition. Such a mechanism results in a supralinear increase of the integrated noise at high recording densities. The noise increase includes the increases of both position jitter and transition length fluctuations. For films with no intergranular exchange coupling, the transition boundary exhibits narrow finger structures and only a very small supralinear increase of the integrated noise results at small bit intervals. Noise correlations between the two transitions in the di-bit pairs are analyzed for the exchange coupled films.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spin-polarized secondary electron microscopy of written domains in CoNiCr and its correlation with noise measurements as a function of write current

Spin-polarized secondary electron microscope images of tracks of magnetic domains, written in Co62.5Ni30Cr7.5 thin-film longitudinal recording media, are presented as a function of write current. The corresponding modulation noise measurements are also presented for this sample. We observe that the magnetic microstructure visible in the images can be correlated with the modulation noise in each region of write current investigated. Explanations for the possible origins of this microstructure are presented.

Noise and bit jitter performance of CoNiPt thin film longitudinal recording media and its effect on recording performance

The authors investigate the hysteretic properties and the recording behavior, such as bit jitter, overwrite, resolution, and on-track and off-track noise, of thin-film media based on a CoNiPt alloy. The films consisted of one alloy composition, sputtered under different process conditions to create films of different microstructure, magnetic hysteresis loop squareness, and coercivities. The factors that contribute to the bit shift are classified as originating from intersymbol interference, overwrite and media noise, on the basis of the results of magnetic recording characterization of the media. Analysis of the microstructure and hysteretic properties indicates that the noise is associated with the formation of magnetic clusters. >