Novel pure spin current injection and detection into graphene via functionalized tunnel barriers and 1D contacts

Abstract

This thesis introduces the study of functionalized graphene (f-Gr) and its anisotropy. An initial objective is to distinguish its properties from the pristine graphene case. Manipulation of graphene is of interests since it is a material with much promises for the field of spintronics, mainly because its metal-semiconductor attributes. One attribute is its capability as medium for spins to travel while they remain relatively unaffected resulting in large spin relaxation lengths. This part of the work is dedicated towards further manipulation of graphene in spintronic devices and its possible magnetic properties. To address the latter, magnetic moment formation is induced on the surface of graphene by reacting a molecule named Benzoyl peroxide (BPO). The magnetic moments provide an exchange field. This topic is studied by controlling the density of BPO defects that are physisorbed on top of graphene and fixed onto it by means of a photochemical reaction using a 532 nm laser. The techniques used to probe the graphene are charge and spin-transport measurements at room and low temperatures. Via a second method, we study the anisotropy level of this f-Gr system. We do this with help of non-local spin-precession measurements (Hanle configuration) where the key is to measure at different angles β with respect to the normal plane to the sample which is defined as β = 90 °. The result of these two approaches is studied by analysis of extracted parameters which are relevant to spin transport. Preliminary results reveal that our f-Gr does indeed present magnetic moment formation although it is a rather paramagnetic behaviour since it is largest as T → 0 K. In regards of anisotropy a slight anisotropy is detected of the ζ < 1 type, meaning τ⊥ < τ∥ which is consistent (at least within the range of temperatures studied) with in-plane spin-orbit-coupling fields along the graphene plane. A third method involves the study of a modified functionalized system where f-Gr sits on top of an atomically flat surface, hexagonal boron nitride (hBN), to then be functionalized. Charge transport as well as magnetoresistance techniques are used to study quantum interference phenomena. Results indicate weak localization occurs in hBN/f-Gr as predicted from theoretical works besides confirming the presence of magnetic moment formation thanks to the BPO molecules.

Date of Award	31 Oct 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Irina Grigorieva (Supervisor) & Ivan Vera Marun (Supervisor)