Magnetic Proximity Coupling to Transition Metal Dichalcogenide
- Author(s): Tsai, Shiao-Po
- Advisor(s): Wang, Kang Lung
- et al.
Two-dimensional material family is long time potential semiconductor candidate material system, for its ability to suppress short channel effect while scaling gate length. For a long time since the graphene monolayer exfoliation successfully in 2004, the researches in the field focused on charge-orientated devices such as thin film transistors, negative capacitance transistors, or applying its atomic thin thickness as quantum barrier for tunneling devices. Recently, because of more characterizations discovered in its special crystal structures, researches of spin and magnetism manipulations in 2-D material become prospering. Still, as a emerging stage of the field, little understanding of the mechanism inside is always the most significant challenge.
In this dissertation, the author focused on introducing magnetism into MoS2, one of transition metal dichalcogenides, through magnetic proximity effect (MPE). In chapter 2, the author demonstrated room temperature proximity-induced spin polarization in MoS2, with yttrium iron garnet (YIG) as magnetic proximity host, which was the firstly demonstrated in the world. In this chapter, the author also demonstrated the importance of shallow state in MoS2 for magnetism introduction through spin resolved photoluminescence (SR-PL). In 2-4, white light magnetic circular dichroism (MCD) was implemented to further characterize the inner mechanism of MPE. Through the MCD results, the mechanism between MoS2/YIG heterostructure was confirmed to be antiferromagnetically exchange coupling. The reference MCD of YIG and MoS2/Al2O3/YIG further verified the MPE induced MoS2 spin polarization. It was the first time people have better scope of the mechanism of MPE. In the end of this chapter, an illustration of band structure is given as explanation for the charge transfer mechanism and the resulting antiferromagnetically exchange coupled MoS2 and YIG’s magnetic moments. In chapter 3, the antiferromagnetic MPE was studied based on the foundation of chapter 2. An AFM perovskite, SmFeO3, was selected as MPE host in this experiment. The SR-PL results showed the significance of uncompensated spin contribution in SmFeO3/MoS2 heterointerface. The strong external field SR-PL also demonstrated the magnetic canting effect in AFM proximity effect is only crucial when uncompensated spin plane of host is presented. The results showed the proximity effect triggering in TMD is extremely crucial from the very interfacial atomic layer of host. In the last chapter, the author lists several potential future works in this field.