Doctor of Philosophy (Ph.D.)
Degree Granting Department
Manh-Huong Phan, Ph.D.
Hariharan Srikanth, Ph.D.
Humberto Rodriguez Gutierrez, Ph.D.
Sarath Witanachchi, Ph.D.
Jing Wang, Ph.D.
ferromagnetism, heterostructures, spintronics, transition metal dichalcogenides
Atomically thin transition metal dichalcogenide (TMD) semiconductors hold enormous potential for modern optoelectronic devices, magnetic sensing, and quantum computing applications. By inducing long-range ferromagnetism (FM) in these semiconductors by stacking them with other magnetic TMDs or through the introduction of small amounts of a magnetic dopant, it is possible to extend their potential in emerging spintronic applications. In this dissertation, we aim to demonstrate two important applications of these materials: magnetic sensing and light-mediated, room temperature (RT) FM in V-doped WS2 (V-WS2) and V-WSe2 monolayers and in ML VSe2/TS2 (T = Mo and W) heterostructures. In this work, we developed a new ultrasensitive magnetometer using the principle of magneto-LC resonance, which employs a soft ferromagnetic Co-based microwire coil driven near its resonance in the radio frequency (RF) regime. The combination of LC resonance with an extraordinary giant magneto-impedance effect renders the coil highly sensitive to changes in the magnetic flux through its core. By placing the sample at the core of the coil we can probe its magnetic permeability. This technique allows us to easily apply external stimuli to the samples as we perform real time measurements. Using this magnetometer, we have measured light intensity dependent magnetic permeability of the V-WS2 (V-WSe2) monolayer subject to light illumination, confirming light control of RT magnetism in this material. Guided by density functional theory calculations, they attribute this phenomenon to the presence of excess holes in the conduction and valence bands, as well as carriers trapped in the magnetic doping states, which mediates the magnetization of the V-WS2 (V-WSe2) monolayer. We have also used this technique to demonstrate light-mediated FM at RT in ML VSe2/MoS2 or VSe2/WS2 heterostructure. This effect is attributed to photon absorption at the MoS2 or WS2 layer that generates electron-hole pairs mediating the magnetization of the VSe2/MoS2 or VSe2/WS2 heterostructure, and we demonstrate the direct role of confinement effects in enhancing light-mediated magnetism in this heterostructure. In addition, we have demonstrated the potential of VSe2/MoS2 heterostructures for magnetic sensing by exploiting the large change in resonance frequency of the probe in the presence of an external magnetic field, an effect that is further enhanced by inserting VSe2/MoS2 in the core of the sensor. We have also demonstrated the potential of exploiting the AFM spin coupling between V and W atoms in V-WSe2 monolayers, which results in the formation of two magnetization states when an external magnetic field is swept. This magnetic switching feature shows the potential of V-WSe2 monolayers for energy harvesting applications.
Scholar Commons Citation
Ortiz Jimenez, Valery, "Light-Controlled Magnetism and Magnetic Sensing in Two-Dimensional Vanadium Dichalcogenides and Related Semiconductors" (2022). USF Tampa Graduate Theses and Dissertations.