Domain Walls, Demagnetizing Fields and Anisotropy in Thin Ferromagnetic Films

Citation

Collette, René Clément (1964) Domain Walls, Demagnetizing Fields and Anisotropy in Thin Ferromagnetic Films. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/BSKM-G135. https://resolver.caltech.edu/CaltechETD:etd-09122002-092748

Abstract

The so-called Neel walls separating antiparallel domains in very thin ferromagnetic films are found, on the basis of accurate calculations, to have a shape differing significantly from the linear rotation model suggested by Neel. In this 180 [degree] rotation, three regions can be distinguished: a central one where the magnetization [...] rotates rapidly (positive demagnetizing energy) and two adjacent regions extending in the neighboring domains where the rotation is very much slower. In these "tail" portions of the curve, the direction of [...] is determined mostly by a balance between the anisotropy torque and the torque due to the internal field. The calculations have been performed for permalloy films with thicknesses ranging from 0 to 200 [angstroms]. The walls extend up to several microns, in each of the adjacent domains (of the order of 15 [microns] at a thickness of 200 [angstroms]. As a continuation of the study of infinite Neel walls, the case of double walls (360 [degree] rotation) and of cross-tie walls is also analysed on a semiquantitative basis. The main characteristics of these two configurations can be explained on the basis of the new model found for the pure Neel walls. In a second section, the internal demagnetizing field H[subscript i] is calculated as a function of the shape, the thickness and the edge profile of the film. Along the edges perpendicular to the easy direction, the growth of peaks of reverse magnetization is studied when the external field varies. Also the detailed configuration of the internal field at the edge is found to depend strongly on the profile of the latter. By varying the slope of a tapered edge, it is shown that (H[subscript i])[...] can be reduced to such a small value that nucleation will take place only at an external field larger in absolute value than the normal coercive force of the film. Thus the hysteresis curve along the easy direction is noticeably altered and very square. In a third section, an instrument is presented for the study of the magnetic anisotropy in the plane of the film. This apparatus is particularly suitable for determining the anisotropy field, the single domain state being preserved at all times

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