Bitter Technique Research Articles

Domain-Wall Structure in Permalloy Films

Domain-wall structure in Permalloy films in the thickness range 25 to 2000 A has been studied by the Bitter technique. A new type of 180° wall has been observed: the main wall is cut at regular intervals by short, right-angle ``cross ties'' which terminate in free, single ends. The cross-tie period and length are dependent on film thickness, each becoming shorter with decreasing thickness. These patterns can be understood in terms of a new model for the structure of domain walls in thin films of low-anisotropy material. In the conventional model the atomic moments within the wall rotate about an axis perpendicular to the wall. In a thin film such a configuration leads to a large energy contribution from the large demagnetization factor normal to the film. In the new model, the axis of rotation is itself thought to rotate about the axis of the wall to give a ``corkscrew'' configuration of spins and a large decrease in associated magnetostatic energy. Of several experiments which have been performed which support this model, one is briefly described.

Growth of MnBi Crystals and Evidence for Subgrains from Domain Patterns

MnBi crystals have been prepared by crystallization in a temperature gradient from a liquid solution of bismuth saturated with manganese. Informative domain patterns have been developed on surfaces of a crystal by the normal Kerr magneto-optic effect and by the Bitter technique. Block patterns, obtained in some instances, have been interpreted as evidence for subgrain structure.

A Study of Bitter Figures using the Electron Microscope

The Bitter figure technique is modified to give patterns in the form of thin films which can be removed from the specimen and examined by high power phase-contrast microscopy and by electron microscopy. This makes possible the observation of extremely fine detail and direct measurement of the width of domain walls.

A Study of Domain Structures in Alnico

The Bitter figure technique is used to study domain structures on polycrystalline alnico specimens with coercivities ranging from 0 to 100 oersteds, in which recognizable domains are recorded. In low coercivity specimens the domains are bounded by comparatively straight walls but they show more irregular outlines in high coercivity specimens.