Wall Motion Reversal in Easy-Axis-Coupled Film Strips

Abstract

Wall motion reversal of the magnetization in coupled film strips is examined theoretically and experimentally. The structure is a conductor strip sandwiched between two Permalloy strips having their easy directions across the strips. If a train of current pulses of sufficient amplitude passes through the conductor strip, the Permalloy layers may be switched around the conductor in either of two sense depending on the polarity of the current. Criteria are presented for coupling (that is, that the two layers remain essentially oppositely magnetized) as a function of width of the strip, thickness of the Permalloy, coercivities of the films, and thickness of the intermediate conductor. It is found that coupling may break down either if the strip is too narrow or too wide. For strips which are coupled and have relatively thin enclosed conductor layers, the multiple-pulse field necessary to switch the film strip is about the average of the coercivities of the two Permalloy layers. For thicker conductor layers, this field is reduced by a geometric factor accurately predicted by a model using only magnetostatic interactions between the two Permalloy layers. Data are presented for 2000-Å layers of Permalloy in 0.125- to 4-mm strips with separations between the Permalloy strips between 0.6 and 8.6 μ. The coercivities of the films range between 0.6 and 6 Oe.