Interplay of Charge Current and Spin in Nanostructures

Abstract

Controlling magnetization on short time scales and/or small dimensions is a hot topic in the field of spintronics, owing to its fundamental physics and its applications for information technology. The most straightforward way to control magnetization is by using an external magnetic field. However, because of the technical limitation in using a magnetic field at smaller sizes and larger amplitudes, alternatives have been investigated such as using currents or light to control the magnetization. In this thesis, we study the interplay of current and spin in nanostructures. The charge current, in the work of this thesis, is generated by shining circularly polarized light on conducting rings, or by applying a voltage to magnetic wires. We use the Lagrangian multiplier method to obtain the Hamiltonian of the system in the presence of the current quantum mechanically. In the first part of the thesis, we study the effect of the current on the magnetization of a system. We demonstrate that circular current has the potential to generate or change the magnetization in certain systems, when the spin orbit interaction is present. Moreover, we study the current-induced motion of pinned domain walls, by only using energy considerations. The second part of this thesis focuses on an opposite effect, viz. the conductance controlled by the spin orbit interaction in an array of rings, an effect known as Aharonov effect. We demonstrate that the oscillations for arrays of rings with different average radii are in good agreement with the experimental as well as the theoretical results obtained for a single mode ring strongly coupled to the leads. We suggest experiments to distinguish between these fundamentally different theoretical models.