2264 IEEE TRANSACTIONS ON MAGNETICS, VOL. 39, NO. 5, SEPTEMBER 2003 Transition and DC Noise Characteristics of Longitudinal Oriented Media G. Choe, B. R. Acharya, K. E. Johnson, and K. J. Lee Abstract—Transition and dc noise characteristics of longitu- dinal recording media were studied as a function of orientation ratio (OR). With increasing OR, a substantial decrease of dc noise is observed against the gradually increasing transition noise, resulting in the reduced media total noise. The increase in the media transition noise with OR is attributed to the increase in the cross-track correlation length . The experimentally estimated for the media with is significantly larger than that of the media with , possibly resulting from the difference in magnetostatically coupled Co grains aligned to the track direction. For high-density low designs, reducing dc noise by increasing OR, in spite of an increase in transition noise, becomes an effective means to increasing areal density. Index Terms—DC noise, magnetic recording media, orientation ratio, signal-to-noise ratio, transition noise. I. INTRODUCTION R EDUCING media noise becomes more important as recording areal density increases. Our recent report on highly in-plane oriented media indicated that in-plane orientation ratio (OR) improves recording performance at high-recording densities by reducing the width of the switching field distribution as well as the energy barrier distribution [1]. However, there has been disagreement over media noise performance of high OR media. Zhu et al. reported modeling data that predicts good recording performance of high OR at low density but sharply degraded performance at high density due to percolation of adjacent transitions [2]. More recent simulation results suggested that transition noise power is reduced for high OR media and is strongly dependent on the magnetization reversal mechanism [3]. On the other hand, Zhou and Bertram reported that the cross-track correlation length increases slightly with increasing OR in the presence of modest exchange coupling and that dc noise decreases with OR, but they made no statement about whether high OR is desirable [4]. In this paper, we experimentally investigated dc and transition noise characteristics of media with various OR values and we conclude that, indeed, high OR is critical to media performance. The observed results suggested that with increasing OR, dc noise is significantly reduced, while the media transition noise gradually increases. As a result of significant dc noise reduction to the total media noise, the Manuscript received December 27, 2002. G. Choe, B. R. Acharya, and K. E. Johnson are with the MMC Technology, San Jose, CA 95131 USA (e-mail: gunnchoe@mmctechnology.com). K. J. Lee is with the Samsung Advanced Institute of Technology, Suwon, Korea. Digital Object Identifier 10.1109/TMAG.2003.816266 Fig. 1. Normalized dc noise, normalized media total noise, and normalized media transition noise as a function of OR. normalized total media noise power of higher OR media is lower over a wide range of recording densities. II. EXPERIMENT The media were sputtered on textured Al/NiP substrates using an Intervac MDP 250B system. The sputtered films consist of a Cr, a CrMo based underlayer, a CoCr-based inter- mediate layer, magnetic CoCrPtB double layers, and a carbon overcoating layer. OR was controlled by adjusting the textured NiP surface morphology resulting in different “line density” indicated by the depth of texture line-to-the average distance between texture lines. The same magnetic layered films were deposited onto the mechanically textured substrates. All the media with different OR values were fabricated to have the same and of 4000 Oe and 0.35 memu/cm . Dynamic electrical recording performance was measured on a Guzik spin stand using a merged giant manetoresistive (GMR) read/write head with magnetic write width of 0.24 m and magnetic read width of 0.14 m. III. RESULTS AND DISCUSSIONS Fig. 1 shows the dc noise as well as the total media noise (1-T integrated noise at 680 kfci dc noise) normalized to isolated signal for the different OR media. As shown in the plot, both the dc noise and the total media noise decrease with increasing OR. This OR dependence of is opposite to the reported mi- cromagnetic simulation results [2], [4], although the dc noise change with OR agrees well between our experimental data and 0018-9464/03$17.00 © 2003 IEEE