Recording Study Of Isotropic Versus Anisotropic Media With MR Head

Abstract

Narow track recording with MR head is being used for increasing areal density in longitudinal recording media. However, recording with MR head has shown track edge hooks with wide erase bands particulaty at high skew angles in circumferentially textured (anisotropic) media [I]. This not only reduces the available area for recording data, but also poses problem in servo tracking. To investigate this effect we prepared both isotropic and anisotropic media and investigated track edge noise at different head skew angles.CoCrTa longitudinal media with an Mrt of about 0.8 memu/cmz and a coercivity of 2400 Oe were prepared by using NiPlAl substrates. Magnetic film thickness and substrate roughness (Ra) were found to have significant influence on orientation ratios of Hc and Mr. The OR of Hc was found to decrease with decreasing magnetic film thickness and Ra of substrate. For the media prepared on smooth untextured surface ( fig.1 .a) the Hc and Mr were isotropic in the film plane, whereas for the medium prepared on circumferentially textured substrates (fig 1 .b) with an Ra of 47 A the OR of Hc was 1.3forthickerfilm (M,t=2.0 memulcm2) and 1.13 for thinnerfilm (Mrt = 0.8 memulcmz).The recording measurements were performed on these media with an MR head of 3 urn track width at 0 and 10 degree skew angles. The recording was done at different linear densities up to 180 kfci. No track edge hooks were observed but partial erasure was present at 140 kfci and above ( fig. 2.a &b). Standard low frequency TAA showed that isotropic media is about 15% lower in amplitude at both skew angles ( fig. 3a). On the other hand the overwrite was 3 to 4 dB higher for the isohpic media. RMS noise was measured (140 kfci) at various offtrack locations for both the disks at both skew angles. We found that the ontrack RMS noise is roughly proportional to the low frequency signal amplitude in all cases, which reveals in similar SNR. The offtrack noise is modelled by sum of track noise and edge noise. Here, track noise is defined as the noise contributed by the fraction of the track under the head assuming that it has the same noise property as the track center, which means that its power is proportional to the signal amplitude. The edge noise power is calculated by subtracting track noise power from the measured offtrack noise power. We found that the edge noise is significant in both disks that the noise does not reduce at the same time as signal when read head moves offtrack. However, when normalized with the ontrack low frequency signal amplitude, the RMS edge noise is quite similar in all cases except that the isotropic disks seems to have larger noise far from the track (fig. 3b).The study revealed that isotropic media can be prepared on smooth untextured substrates and when 0.R is small, both anisotropic and isotropic media show similar track edge noise characteristics independent of skew angles.