Magneto-transport studies in WTe2/Cr2Ge2Te6 bilayers

Abstract

The recent discovery of two-dimensional (2D) ferromagnetic insulators and the continuous advancements in the fabrication of van der Waals heterostructures have enabled studying proximity-induced magnetic exchange interactions. Stacking a vdW magnetic insulator like Cr2Ge2Te6 (CGT) with a 2D semimetal with strong spin-orbit coupling (SOC) like WTe2 could potentially allow us to imprint magnetism in the latter, a physical property absent in its pristine form. This thesis presents a detailed investigation of magnetic proximity effects through magnetotransport studies in hybrid WTe2/CGT hetero-bilayers. This material combination could represent a building block towards realizing the quantum anomalous Hall effect, which requires the co-integration of a topological insulator, like monolayer WTe2, with a perpendicularly magnetized 2D ferromagnet such as CGT. Six devices were fabricated and electrically characterized. We observe that the annealing of the heterostructure after preparing the bilayer is a crucial step for improving the quality of the vdW interface between WTe2 and CGT. Additionally, an increase in the Curie temperature of CGT, likely driven by spin-orbit coupling interfacial effects, has been observed. Notably, four out of the six annealed samples exhibited magnetic hysteretic behaviour in the transversal voltage Vxy. The angle dependence of the magnetoresistence in one sample was analysed to investigate whether the hysteric behaviour in Vxy arises from proximity-induced anomalous Hall or spin Hall magnetoresistance effect, using the spin texture in the low-symmetry WTe2.