In order to investigate 2D layers potential for spintronics, we fabricated 3D crystals of different layered materials as Transition Metal Dichalcogenides (MoS2, WSe2, ZrS2, ZrSe2, WTe2…) and the antiferromagnetic Transition Metals Thiophosphates (FePS3, NiPS3, MnPSe3…) by chemical vapour transport (CVT) technique. Thin flakes down to the monolayer could be obtained for most of these materials (Figure 1). We also investigated the possibility to modify their properties towards multifunctional devices by the fabrication of multilayers stacks heterostructures or the chemical functionalization of the thin layers with spincrossover nanoparticles or Prussian Blue (PB). MoS2 functionalization with PB revealed to be of particular interest for energy application in batteries, giving rise to a publication.
The fabricated 2D materials were structurally characterized by AFM and Raman spectroscopy to determine their quality and flakes thickness. XPS characterization using synchrotron radiation was also performed in order to study their oxidation under ambient conditions. These studies are interesting by their own since the properties of these 2D materials are still mostly unexplored. Electrical characterization of the 2D layers was also performed through the fabrication of lateral devices, while vertical transport was characterized using a conductive tip AFM (CT-AFM). Finally, magnetic characterization of antiferromagnetic FePS3 2D flakes was performed by low temperature Raman spectroscopy and revealed that magnetic ordering was maintained down to the thin layers.
Next, we developed a process for implementing 2D materials in magnetic tunnel junction devices. This process allows using room temperature ferromagnetic materials as bottom electrode (e.g.: Co or NiFe), while avoiding their exposition to the air and thus their oxidation. This represents an important advance compared to state of the art MTJs fabrication with mechanically exfoliated flakes. We initially focused on MoS2 as the prototypical 2D material behind graphene, also motivated by its air stability. We successfully fabricated Co/MoS2/Co MTJs and performed magneto-transport measurements. A magnetoresistance signal up to room temperature could be detected in these devices (Figure 2). These promising results contribute to the understanding of spin injection mechanisms in MoS2 and open the way towards the implementation of other 2D materials in MTJs.
This work has already been presented in 7 international conferences or workshops and it has given rise to 2 publications. Two more publications are currently in preparation or submitted.
