Study of field-driven wall-configuration conversions for laminated permalloy in the easy-axis state

Laminated Permalloy, with edge-curling walls replacing closure domains, has been proposed to increase permeability and reduce wall noise in recording. However, in structures meeting the criteria for Slonczewski's "easy-axis" state, normal walls often coexist with edge-curling walls. We have used our laser magneto-optic microscope to study inductive-head-yoke shaped elements of two and four Permalloy layers separated by nonmagnetic, metallic spacers. In the four-magnetic-layer sample a state with a single wall, terminating at the edge-curling regions and lying along the easy-axis direction, is often observed on the top and bottom layers. Some elements may be driven into an easy-axis state with no observed domain walls. The two-magnetic-layer sample also exhibited simultaneous one-wall structures on the top and bottom layers. The other stable configuration was a no-wall state on the top layer and a two-wall (three-domain) state on the lower layer. These "coupled" states were exceptionally stable in both samples; fields on the order of 300 Oe were required to switch between configurations.