We study current-induced domain wall dynamics in a thin ferromagnetic nanowire. We derive the effective equations of domain wall motion, which depend on the wire geometry and material parameters. We describe the procedure to determine these parameters by all-electric measurements of the time-dependent voltage induced by the domain wall motion. We provide an analytical expression for the time variation of this voltage. Furthermore, we show that the measurement of the proposed effects is within reach with current experimental techniques. We also show that a certain resonant time-dependent current moving a domain wall can significantly reduce the Joule heating in the wire, and thus it can lead to a novel proposal for the most energy efficient memory devices. We discuss how Gilbert damping, non-adiabatic spin transfer torque, and the presence of Dzyaloshinskii-Moriya interaction can effect this power optimization. Furthermore, we propose a new nanodot magnetic device. We derive a specific time-dependent current that is needed to switch the magnetization of the nanodot the most efficiently.

The magnetic behaviour in nanoscale structures is of great interest for the fundamental understanding of magnetisation processes and also has importance for wide ranging technological applications. This thesis examines mechanisms for the enhanced control of domain walls in these structures via focussed ion beam modifications to magnetic nanowires and through the inclusion of periodic geometrical modifications to the nanowires geometry. A detailed investigation into the effect of focussed ion beam irradiation on the structure of NiFe/Au bilayers was performed through x-ray reflectivity and fluorescence techniques. This analysis revealed the development of interfacial intermixing with low dose irradiation. This is associated with complex changes of the magnetic behaviour including a rapid decrease, followed by a recovery of the saturation magnetisation with low dose irradiation. This behaviour is attributed to changes in the local environment of the atoms at the interface; resulting in modifications to the magnetic moment on Ni and Fe. The development of an induced moment on Au and a change in the spin-orbit interaction is also suggested. Localised control of the magnetic properties in nanowires demonstrates the ability to manipulate domain walls in these structures. Here, irradiated regions provide pinning sites where the width and dose of the irradiated region give control over the pinning potential. The inclusion edge modulation to nanowires geometry provides additional control over their magnetic behaviour. The direct magnetisation reversal field of these structures is explained by an analytical model based on the torque on the spins following the modulated wire geometry. This model is scalable for different modulation parameters and combines with the effect of localised regions of orthogonal anisotropy along the wire; explaining the reversal behaviour over the entire parameter space. Domain wall mediated reversal in modulated wires was also investigated in these structures. The inclusion of modulation shows an improvement in dynamic properties by the suppression of Walker breakdown. This is due to the relationship between geometrical modulations and the periodicity of micromagnetic domain wall structural changes during the Walker breakdown process. The combination of this work shows a route to the optimisation of the dynamic properties whilst minimising the detrimental increase in the de-pinning field from the modulation.

Dynamical behavior of magnetic domain wall (DW) is one of the main issues in the field of spintronics. In this chapter, several experimental studies in DW dynamics in nanomagnetic systems are described. For the study of DW motion in nanoscale wires, samples with a trilayer structure, ferromagnetic/nonmagnetic/ferromagnetic, were prepared and the position of DW was estimated from electrical resistance measurements using giant magnetoresistance principle. The velocity of DW driven by an external field has been evaluated from the resistance change. On the other hand, current-driven DW motion in a single wire of ferromagnetic layer was studied by magnetic force microscopy (MFM). All-electrical control and local detection of multiple magnetic DWs are also shown. Magnetic vortex structures are realized in nanoscale ferromagnetic dot systems. The behavior of vortex core magnetization was observed by MFM. Recent topics such as the switching of vortex core driven by a high frequency AC are introduced. Furthermore, all-electrical operation of a magnetic vortex core memory cell is demonstrated.