On the scaling behaviour of cross-tie domain wall structures in patterned NiFe elements

TL;DR

This study investigates how the structure and density of cross-tie domain walls in NiFe elements change with size and confinement, revealing scaling laws and dynamic modifications under magnetic fields.

Contribution

It provides new insights into the scaling behavior and dynamic modifications of cross-tie domain walls in patterned NiFe elements, supported by Lorentz microscopy observations.

Findings

Cross-tie density scales inversely with the distance to the element edge.

Confinement increases cross-tie density and modifies wall structure.

Dynamic wall modifications involve vortex/anti-vortex pair processes.

Abstract

The cross-tie domain wall structure in micrometre and sub-micrometre wide patterned elements of NiFe, and a thickness range of 30 to 70nm, has been studied by Lorentz microscopy. Whilst the basic geometry of the cross-tie repeat units remains unchanged, their density increases when the cross-tie length is constrained to be smaller than the value associated with a continuous film. This occurs when element widths are sufficiently narrow or when the wall is forced to move close to an edge under the action of an applied field. To a very good approximation the cross-tie density scales with the inverse of the distance between the main wall and the element edge. The experiments show that in confined structures, the wall constantly modifies its form and that the need to generate, and subsequently annihilate, extra vortex/anti-vortex pairs constitutes an additional source of hysteresis.