Shape and Energy of Néel Walls in Very Thin Ferromagnetic Films

Abstract

The so‐called Néel walls separating antiparallel domains in very thin ferromagnetic films are found, on the basis of a precise treatment, to have a shape differing significantly from the linear rotation model used by Néel. In this 180° rotation, three regions can be distinguished: a central one where the magnetization M rotates rapidly and where the demagnetizing energy is positive, and two adjacent regions extending in the neighboring domains where the rotation is very much slower and the magnetostatic energy negative. In these ``tail'' portions of the curve the direction of M is determined mostly by the balance between the anisotropy torque and the torque due to the internal demagnetizing field. The calculations have been performed for Permalloy films with thicknesses ranging from 0 to 200 Å. The walls extend up to several microns in each of the adjacent domains (of the order of 15 μ at a thickness of 200 Å). The energy stored inside the wall is calculated for this new configuration and found to be less than previous approximate results.