The interplay of electronic and magnetic functionalities in entropy-stabilized oxides

Abstract: A unique benefit to entropic stabilization is the increased solubility of elements, which opens a broad compositional space with subsequent local chemical and structural disorder resulting from different atomic sizes and preferred coordinations of the constituents. In the antiferromagnetic entropy-stabilized oxides studied here, we see that by tuning the chemistry, and thus the concentration of local structural distortions, we can either induce or reclaim a large degree of frustration in the magnetic lattice of the material. As the large dielectric response of these materials may be strongly linked to their structure, here we study the interplay of electronic and magnetic functional responses in entropy-stabilized oxides. Our results reveal that the unique characteristics of entropy stabilized materials can be utilized to engineer and enhance magnetic functional phenomena in oxide thin films, as well as offer a powerful platform for the study of defects and functional properties.

Abstract: Ultra-wide-band-gap (UWBG) semiconductors have tremendous potential to advance electronic devices as device performance improves superlinearly with increasing gap. Ambipolar doping, however, has been a major challenge for UWBG materials as dopant ionization energy and charge compensation generally increase with increasing band gap and significantly limit the semiconductor devices that can currently be realized. Rutile germanium oxide (r-GeO2) is a promising UWBG (4.68 eV) material, yet has not been explored for semiconducting applications. Using hybrid density functional theory, we demonstrate r-GeO2 to be an alternative UWBG material that can be ambipolarly doped.

Transition metal dichalcogenide (TMD) monolayers, such as WSe₂, WS₂, MoSe₂, and MoS₂, possess distinct physical properties due to the strong coupling between spin and valley degrees of freedom.(1, 2) As monolayer TMDs have a direct bandgap lying in visible range, they have been studied extensively by optical methods.(2, 3) Heterostructures of monolayer TMDs with other functional materials are currently attracting significant attention due to the opportunities to access and utilize their spin-valley degrees of freedom through electrical means.(4) For instance, TMD-ferromagnet heterostructures have been employed recently to study spin current generation in TMDs. (4, 5) The quality of atomically thin TMDs, however, is strongly affected by deposition techniques of metallic layers and have not been fully investigated.(6) In this work, we report the fabrication of Pt/Co multilayer using pulsed laser deposition (PLD) on monolayer WSe₂ grown bymetalorganic chemical vapor deposition (MOCVD) on single crystalline (0001)-oriented Al₂O₃ substrates. PLD is a plasma based deposition technique capable of tuning of kinetic and thermodynamic conditions over an expanse range to elucidate and control fundamental structure-property relationships across a wide variety of material classes. (7)Using Raman Spectroscopy, we monitor deposition induced damage on monolayer WSe₂. The pressure of Argon process gas is found to suppress deposition induced defects in WSe_2, which indicates that the primary source of defect generation comes from ion bombardment. Further, we report on magnetometry and spin torque measurements of our WSe₂-ferromagnet heterostructures and demonstrate the generation of spin current from TMD layer.  We anticipate that our results will advance the electrical investigation of spin-valley and spin generation phenomena in 2D hybrid heterostructures for spintronics.