Quantum transport in magnetic nanostructures

Author(s)

Imara Lima Fernandes

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2015-06-30

Examining board members

Guillermo Gerardo Cabrera Oyarzún; Cesar Augusto Dartora; Fernando Assis Garcia; José Antonio Brum; Carlos Manuel Giles Antunez de Mayolo

• Advisor: Guillermo Gerardo Cabrera Oyarzún

Abstract

In this work, we have studied the spin-dependent quantum transport in magnetic nanostructures. The main structures studied are magnetic tunneling junctions and systems composed of an arrangement of quantum dots coupled to ferromagnetic electrodes. Using the nonequilibrium Green's function techinique, we were able to calculate selected properties of the systems such as the electric current, the spin current, local density of states and the current-induced spin-transfer torque. In the first system, we have observed the effects of the spin-flip scattering in the transport properties considering tunneling junctions composed by an insulating layer between two ferromagnetic electrodes. The results obtained for this system showed that the magnetoresistance is related to density of state effects at the ferromagnetic electrodes, and we have found that it is strongly affected by the spin-flip scattering. Besides, we also observed that the spin-flip scattering gives rise to an additional spin-torque to the system. For the system composed of two quantum dots T-shaped electrodes coupled to ferromagnetic electrodes, we investigated the spin-dependent properties. We have observed that the appearance of the Fano resonance and the formation of bound states rely strongly on system parameters. Another interesting finding is the possibility to control the electrical conductance via a gate voltage. We figured out that changing the energy level of the central dot affected directly the Fano resonance peak intensities. Lastly, we have showed that for the system composed by a quantum-dot with two energy levels coupled to two ferromagnetic electrodes must be modified when the \textit{e-e} and the Rashba spin-orbit interaction are taken into account. The Rashba interaction induces level transitions with spin-flip resulting in interesting properties in the spin-dependent transport. We have found out that the spin-orbit interaction strongly contributes to the spin current even for non-magnetic electrodes (AU)

• FAPESP's process: 11/19298-4 - Quantum transport in magnetic nano-structures
• Grantee: Imara Lima Fernandes
• Support Opportunities: Scholarships in Brazil - Doctorate