Dilute Magnetic 2D-Semiconductors: Fundamentals for Device Applications

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Non-technical DescriptionMagnetic semiconductors are materials with magnetic properties that are also semiconductors. They can be utilized in applications such as non-volatile memories and enable spin-based electronics with applications such as quantum computing. However, most semiconductors are non-magnetic. There has been some success in making magnetic semiconductors through doping conventional semiconductors with magnetic impurities. Usually only low magnetic transition temperatures have been achieved, limiting potential applications. This project will investigate two-dimensional (2D) magnetic semiconductors that have the potential to reach room temperature magnetism. 2D materials are extended in a plane but are only a few atoms thick. Such planar materials have potential for future devices because two-dimensional crystals can be stacked with atomically sharp interfaces. 2D materials are also sensitive to their environment and thus their properties can be tuned through interfaces or external stimuli. In this research the fundamental properties of magnetic dopants in 2D materials will be investigated in order to gain insight on the mechanisms that allow introduction and tuning of magnetism in these materials. The ultimate goal is to develop reliable approaches to realize 2D magnetic semiconductors that function above room temperature. The research has the potential to lead to the development of tunable spintronic devices based on new multifunctional materials. Importantly, this project provides training for graduate students in contemporary materials science with technological relevance and will broaden their experience through international collaborations and research activities.Technical DescriptionThis project explores magnetic dopants in the 2D-semiconductors MoS2 and WSe2. Doped films and monolayers will be grown by low temperature-molecular beam epitaxy to enable the efficient incorporation of various transition metal dopants. The successful doping and the atomic scale dopant-structures will be investigated by scanning tunneling microscopy and spectroscopy to gain insight on the dopant induced defect states that control the local magnetic moments. The role of dopant-element, structure, and concentration on the magnetic properties is investigated by systematically varying materials processing conditions and investigation of the magnetic properties by magnetometry and synchrotron x-ray magnetic circular dichroism studies. The experimental observations are correlated to theoretical density functional calculations. Tunability of the magnetic properties by charge transfer doping in ultrathin films is also studied. This study will give insight on the magnetic coupling mechanism of the dopants and the role of secondary defects in tuning of the magnetism. The study exploits the 2D nature of the material systems for both gaining better insight in the general mechanism for diluted magnetic semiconductors, as well as for the potential of exploiting their atomically sharp interfaces in van der Waals heterostructures for combining magnetic materials with materials with diverse quantum properties as well as for magnetic device structures. Fundamentally, this activity aims at determining the magnetic coupling between magnetic dopants to find the reason for the apparently higher Curie temperatures in 2D magnetic diluted semiconductors compared to traditional semiconductors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.