The effects of head configuration and bias current on the read sensitivity profiles of MR head

Abstract

Intoduction Read sensitivity profiles across the track-width of MR heads were measured using a l pm wide recorded track. The relation between the sensitivity profiles and bias current for heads with different MR configurations is shown. Then, the effects of bias direction and domain states in the MR element are discussed. Exoerimenk The configurations of the MR elements are shown in Figures 1 (a) and (b). MR element (a) has an aspect ratio of 20 and element (b) a ratio of 2. The read active area is shown as the shadowed area and its length (track-width) is 10 pm. The read signal was measured with spectrum-analyzer. A 1 pm wide track was obtained by erasing the original track with 1 pm offtrack. The sensitivity profiles along the track-width direction were measured by scanning the head across the track2 The linear recording density of track was 10.2 kfci. Results and discussion (1) The effect of bias current direction The sensitivity profiles of the heads are shown in Figures 2 (a) and (b). The sensitivity profiles are asymmetric. The magnetization in the MR element slanted by the bias field causes the asymmetry in the profiles, because it gives different torques to rotate the magnetization whether the track is located under the left-side of the element or under the right-side.3 Furthermore, a change of current direction also brings a reverse of the asymmetry. This is due to a reverse of the slant angle of the magnetization. Figures 3 (a) and (b) show the sensitivity profiles of the head in the same current direction. There is little difference between 15 mA and 20 mA in head (a). However, in head (b), the broadening at the left side is apparent when the current increases to 20 mA. We think that this broadening is caused by the domain structure. The MR element in head (b) has a closure domain in the left edge which is insensitive to the signal field. When the current increases, the closure domain reduces or vanishes with the increased bias field. Therefore, the sensitivity in the left edge increases. Head (a) shows little broadening because there is no closure domain in read active area due to its high aspect ratio. (2) The effect of bias current magnitude (3) Sensitivity profile for heads with Barkhausen noise Sensitivity profiles were also evaluated for heads with Barkhausen noise. Abrupt local reductions of the sensitivity were observed. We will discuss the abrupt reduction as results of localized defects, as well as Barkhausen noise.