Magnetization Configurations and Reversal in Small Magnetic Elements

Abstract

This chapter presents an overview of the magnetization configurations and reversal in magnetic structures ranging from a few nanometers to a few micrometers in size that can be described using the theory of micromagnetics. A range of techniques for the characterization of magnetic structures is introduced and the theoretical micromagnetism background, including the energy terms governing the magnetic properties, are discussed. The simplest case of a single domain system with uniform magnetization is treated within the framework of the Stoner–Wohlfarth theory, and experimental examples of such systems are presented. The magnetization configurations in larger systems that exhibit nonuniform magnetization are discussed in detail with a particular emphasis on experimental examples for the geometries that have been studied most often, such as discs, rings, rectangles, wires and pillars. Theoretically, the formation of these states is explained as a result of the interplay between the different magnetic energy terms; multidomain states that occur for larger elements are also introduced. The dynamic properties of the reversal of these elements are addressed, starting with the evaluation of the Landau–Lifshitz–Gilbert equation to obtain the trajectories for single domain particles. This is then extended to cover the nonhomogeneous reversal of nonuniform states. The elementary processes occurring during nonhomogeneous reversal are introduced and used to explain the magnetization reversal in a set of instructive examples.

Vortex magnetic structure in framboidal magnetite reveals existence of water droplets in an ancient asteroid

“…As the magnetic structures of ferromagnetic nanoscale materials depend on their geometry rather than on their intrinsic material properties 20,21 , the magnetic structure of framboidal magnetite should be directly related to the environment in which it was formed and to the processes from which the magnetite obtained it's magnetization. As size increases, the magnetic structure of magnetite changes sequentially from a superparamagnetic state to a single domain, then to a vortex and eventually to a multidomain state.…”

Spontaneous formation of spiral-like patterns with distinct periodic physical properties by confined electrodeposition of Co-In disks

“…Nonetheless, the H C values of the microdisks are considerably higher than those of films featuring analogous composition ( = 136 Oe) 26 . This increase in H C compared to the unpatterned film is possibly due to domain wall hindrances caused by the constrained lateral size of the dots and their reduced thickness 7 49 50 .…”

Correlation between magnetic spin structure and the three-dimensional geometry in chemically synthesized nanoscale magnetite rings

“…6,7 In general, the magnetic properties of ferromagnetic nanoscale elements are governed by the element geometry rather than by the intrinsic materials properties. 8,9 A large effort has been spent studying magnetic states and magnetization reversal mechanisms in such nanostructures in order to find the geometry which provides the simplest, fastest, and most reproducible switching behavior of the magnetization. [8][9][10][11] The magnetization configuration that has raised significant interest is the vortex state in circular elements due to a low influence of edge roughness and due to the zero stray field which makes it promising for applications in high-density storage.…”

“…8,9 A large effort has been spent studying magnetic states and magnetization reversal mechanisms in such nanostructures in order to find the geometry which provides the simplest, fastest, and most reproducible switching behavior of the magnetization. [8][9][10][11] The magnetization configuration that has raised significant interest is the vortex state in circular elements due to a low influence of edge roughness and due to the zero stray field which makes it promising for applications in high-density storage. 1 The highest stability of the vortex state is reached in high-symmetry ring elements where the only source of stray field, namely the highly energetic vortex core is removed.…”