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Daniel Solis Lerma

Proximity-induced transport phenomena in graphene-based spintronic devices

Published on 13 May 2020
Thesis presented May 13, 2020

Abstract:
In this thesis we present a study of the transport properties of a proposed lateral graphene-based spintronic device, composed of two identical magnets on top of a graphene sheet. We investigate in detail, the spin transport in two different magnetic configurations of the magnets: collinear and noncollinear. In particular, we focus on the magnetoresistance phenomena, as well as, the impact of ferroelectricity when the magnets are made of the multiferroic material BFO. We demonstrate the existence of proximity magnetoresistance phenomena (PMR) generating spin current polarization without direct injection trough the ferromagnet and present promising results at room temperature. Moreover, we demonstrate the tuning of the magnetoresistance by the electrical polarization of BFO. Due to the extra degree of freedom, we define two extra physical quantities: the proximity electroresistance (PER) and proximity multiferroic resistance (PMER).
In addition, we provide a theoretical derivation of the spin current conservation equation for the case when the Hamiltonian of the system has spin dependent hoppings and sublattice potential. Lastly we study in detail the spin transfer torque phenomena in the proposed spin valve considering magnets made of YIG, its dependence with respect to size dimensions and calculate the corresponding phase diagram, from which it is possible to estimate the order of magnitude of the current needed to switch the magnetization of the immediate graphene region in contact with the magnet, that for suitable thicknesses, will eventually switch the magnetic orientation of the whole magnet.

Keywords:
non-collinear, graphene, Rashba, spintronics