This thesis investigates the domain wall pinning and depinning in notched nanowires. Both the field-driven and current-driven domain wall depinning and propagation are systematically explored and discussed following a clear thread of thought and series of application oriented proposals are brought up. Basically, three topics are raised and investigated.

Firstly, an empirical energy rule is presented to resolve the issue why pinning exists in a nanowire with inhomogeneities, especially the existence of pinning near an antinotch. As a by-product, the pinning position of a domain wall can be predicted through this rule. This prediction compares well with the simulation results. Based on the pinning at an antinotch, a versatile nanodevice for generating vortices is proposed and numerically...[ Read more ]

This thesis investigates the domain wall pinning and depinning in notched nanowires. Both the field-driven and current-driven domain wall depinning and propagation are systematically explored and discussed following a clear thread of thought and series of application oriented proposals are brought up. Basically, three topics are raised and investigated.

Firstly, an empirical energy rule is presented to resolve the issue why pinning exists in a nanowire with inhomogeneities, especially the existence of pinning near an antinotch. As a by-product, the pinning position of a domain wall can be predicted through this rule. This prediction compares well with the simulation results. Based on the pinning at an antinotch, a versatile nanodevice for generating vortices is proposed and numerically verified.

Secondly, in order to resolve the pinning strength of domain wall against an external field, a general relation between the external field and the magnetic structure around notches is derived based on the energy minimum principle. By estimating the maximum field that holds this relation, we obtain an analytical expression of the depinning field. The results predicted by this relation compare well with the simulation results. Through the relation, we also find that the depinning field depends on types of domain wall as well as geometry of notch. This helps us to come up with the concept of domain wall filters, which are capable to select a desired type of domain wall.

Thirdly, we consider the current-driven domain wall depinning process. Surprisingly, instead of hindering domain wall motion, the notches help domain wall to depin and propagate along a nanowire in the adiabatic limit. The depinning current density is well below the intrinsic pinning current density and the moving distance of domain wall in a notched wire is several times of that in a uniform wire. By delicately designing the distribution of notches, a domain wall is capable to propagate below the intrinsic pinning current. When weak non-adiabatic effect is taken into account, notch can still boost the domain wall motion through the vortex generation in the vicinity of notches. As the strength of non-adiabatic effect becomes strong, the boosting mode disappears and the domain wall motion would be hindered by the notches. Based on the transverse motion of vortex after it’s depinned, the concept of magnetic vortex guide is proposed and numerically realised. Similar to waveguides of electromagnetic wave, the magnetic vortex guides allow a vortex domain wall to move along a nanowire without annihilations at the wire edges.