Magnetic Rings : A Playground to Study Geometrically Confined Domain Walls

Abstract

Geometrically confined domain walls are comprehensively investigated using a range of magnetometry and imaging techniques. The spin structures of head-to-head domain walls are systematically determined and a quantitative domain wall type phase diagrams for NiFe and Co are obtained and compared with available theoretical predictions and micromagnetic simulations. Differences to the experiment are explained taking into account thermal excitations. Thermally induced domain wall type transformations are observed, from which a vortex core nucleation barrier height is obtained. The stray field of a domain wall is mapped directly with sub-10 nm resolution using off-axis electron holography, and the field intensity is found to decrease as 1/r with distance. The magnetic dipolar coupling of domain walls in NiFe and Co elements is studied using x-ray magnetic circular dicroism photoemission electron microscopy. We observe that the spin structures of interacting domain walls change from vortex to transverse walls, when the distance between the walls is reduced. Using the measured stray field values, the energy barrier height distribution for the nucleation of a vortex core is obtained. Finally the pinning behaviour at constrictions is determined.