The Remanent State of Recorded Tapes

Measurements are reported on the in-plane and the perpendicular components of the remanence a tape acquires on passing through the steady field of a recording head. The tape coatings were oriented and unoriented particles of y-Fe,O,, oriented CrO, and unoriented Co-substituted y-Fe,O,. The two writing heads used had 10pmand 2.25pm-gaps, respectively. In each case the in-plane magnetization increases at first with increasing writing current, and eventually reaches a peak that is less than the maximum in-plane remanence produced on the same sample by an electromagnet. For higher values of writing current, in-plane magnetization in the tape actually decreases. The perpendicular remanence is not large enough to explain the difference between the in-plane remanence acquired from the head and the remanence acquired in a magnet. The perpendicular component of the field from the writing head is shown to have two adverse effects on the remanence of the tape. First, it produces a perpendicular magnetization that ranges from 2 percent to 15 percent of the in-plane component. Second, it causes a reduction in the in-plane component to occur near the surface of the tape closest to the writing head. The reduction can be as large as 15 percent of the maximum in-plane remanence and will obviously have an adverse effect on recording performance, particularly at high densities.