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Magneto and Spin Transport in Magnetically Doped Semiconductors and Magnetic Insulators

Yang, Zihao
http://orcid.org/0000-0002-0171-8810
http://rave.ohiolink.edu/etdc/view?acc_num=osu1502963926201783

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Over the last two decades, spin transistors that operate using both charge and spin properties of electrons have motivated extensive studies of injection, detection and manipulation of electronic spin current in various material systems. Dilute magnetic semiconductors, in which the spin polarized charge carriers are coupled to the magnetic moment, are of particular interest due to their compatible lattice structures and similar growth methods to current Si and GaAs technology. The first part of this thesis focuses on the structural, magnetic and magnetotransport properties of magnetically doped GaN and 2D MoS2. The Gd doped AlN/GaN heterostructures are grown by plasma assisted molecular beam epitaxy. The Gd atoms are δ-doped at the AlN/GaN heterointerface where the two dimensional electron gas (2DEG) forms. These samples exhibit defect-induced room temperature ferromagnetism with an easy axis along the c-axis. However, the nonlinear Hall resistivity does not track the magnetization in these Gd doped samples indicating the lack of coupling between the conduction electrons in the 2DEG and the Gd-induced ferromagnetism. This makes Gd doped GaN not useful as a dilute magnetic semiconductor. Mn doped few-layer MoS2 samples synthesized via sulfurization of Mn thin film on sapphire are fabricated in the aim of realizing a 2D dilute magnetic semiconductor. However, these samples mainly show paramagnetism implying the lack of ferromagnetic coupling between the Mn dopants. In addition to the electronic spin current, magnonic spin current has recently received growing research interest since it serves as a new route for achieving novel thermoelectric generators and magnon transistors. The second part of the thesis focuses on the study of the transport properties of the thermally induced magnonic spin current via spin Seebeck effect. A nonlocal opto-thermal spin Seebck configuration is proposed and implemented to measure the spin diffusion length in yttrium iron garnet (YIG). Finite-element modeling (FEM) based on heat and spin transport is employed to validate the detection of the pure diffusive magnonic spin current and to estimate an upper bound of the spin diffusion length by considering the Pt sinking effect from the unused Pt absorbers. Magnon dynamics are probed via the time-resolved longitudinal spin Seebeck effect. The time domain spin Seebeck waveforms consist of a fast rise (~ ns) component and a slow rise (~ ms) component at all temperatures. FEM modeling based on heat and spin transport suggests that the fast rise component is attributed to the interfacial electron and magnon temperature difference while the slow component is a result of bulk magnon diffusion. Different mechanisms (either spin or heat diffusion) are found to dominate the speed of the slow rise component at different temperatures. In the hope of putting the spin heat transport knowledge into practice, a novel Nernst thermoelectric generator with scalable power output using Galfenol wire in a coil geometry is demonstrated. The Nernst coefficient found in Galfenol is the highest among similar ferromagnetic materials. At last, the coupled thermal and condensed magnon transport are modeled to facilitate the design of the magnon Bose-Einstein experiment.
Roberto Myers (Advisor)
Joseph Heremans (Committee Member)
Tyler Grassman (Committee Member)
199 p.
Electrical Engineering; Materials Science
Dilute Magnetic Semiconductor, Spin Saloritronics, Magnon Transport

Recommended Citations

Citations

  • Yang, Z. (2017). Magneto and Spin Transport in Magnetically Doped Semiconductors and Magnetic Insulators [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1502963926201783

    APA Style (7th edition)

  • Yang, Zihao. Magneto and Spin Transport in Magnetically Doped Semiconductors and Magnetic Insulators. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1502963926201783.

    MLA Style (8th edition)

  • Yang, Zihao. "Magneto and Spin Transport in Magnetically Doped Semiconductors and Magnetic Insulators." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1502963926201783

    Chicago Manual of Style (17th edition)

osu1502963926201783
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© 2017, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.