Studies on Quantum Transport and Magnetic Properties of Novel Materials
Restricted (Penn State Only)
- Author:
- Min, Lujin
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 04, 2023
- Committee Members:
- Chaoxing Liu, Outside Field Member
John Mauro, Program Head/Chair
Venkatraman Gopalan, Dissertation Co-Advisor
Zhiqiang Mao, Chair & Co-Dissertation Advisr
Morteza Kayyalha, Outside Unit & Field Member
Ismaila Dabo, Major Field Member - Keywords:
- Quantum transport
Magnetism
Nonlinear Hall effect
High entropy material - Abstract:
- Novel materials with intriguing functionalities are at the forefront of scientific research and technological advancements, often pushing the boundaries of what we perceive as possible. Especially within the realm of materials showing exotic electrical transport and magnetic properties, continuous breakthroughs are being made. These materials can possess unconventional properties and behaviors, such as high-temperature superconductivity, large anomalous Hall effect, quantum anomalous Hall effect, giant magnetoresistance, and multiferroic. Their unique characteristics have directly promoted the development of faster electronic devices, advanced data storage solutions, high-sensitivity sensors, and even quantum computing. Over the past two decades, two new concepts revolutionized the design strategies of functional materials, which are the Berry phase in quantum mechanics and high entropy stabilization in thermodynamics. The Berry phase and related concepts like Berry curvature provide invaluable insights into electronic band structures in the momentum space. It not only explains the long-time puzzled questions like the intrinsic origin of the anomalous Hall effect, but also predicts and underpins a plethora of new electrical transport phenomena and states of matter, such as spin Hall effect, quantum anomalous Hall effect (Chern insulator), topological insulator, Dirac and Weyl semimetals, and valleytronics. Concurrently, the concept of high entropy effect focuses on the crystal structure in real space. By harnessing the large configurational entropy, which arises from placing multiple elements in nearly equivalent concentrations at the same lattice position, a new class of materials is created, termed high-entropy materials. This strategy has led to the discovery and design of many new types of compounds and alloys. A broad spectrum of the functionalities of high entropy materials has been explored recently. Among them, the magnetic property is particularly interesting, as the high entropy tuning can introduce extensive spin disorders by mixing different magnetic and non-magnetic elements, leading to an ideal playground to investigate magnetic materials. In this dissertation, 4 distinct novel materials with compelling electrical transport or magnetic properties are studied, including Dirac material BaMnSb2, focused ion beam deposited (FIBD) platinum (Pt), high entropy kagome topological magnet (Gd,Tb,Dy,Ho)Mn6Sn6 (HE166), and high entropy ferrimagnetic oxide (Mg,Mn,Fe,Co,Ni)xFe3-xO4 (AxFe3-xO4). The main results presented can be categorized into two sections: In the first section, a new type of Hall effect without breaking the time-reversal symmetry, the so-called nonlinear Hall effect (NLHE), is studied with BaMnSb2 and FIBD-Pt. Interestingly, the NLHE observed in these two materials respectively originate from the intrinsic band topology (Berry curvature dipole, BCD) and the extrinsic asymmetric scattering. As such NLHEs occur near room temperature, we also explored their possible applications. In the latter section, the research emphasis shifts to the modulation of magnetization through the high entropy effect. Based on TbMn6Sn6 and Fe3O4, we have designed and synthesized two new high-entropy single-crystalline materials by mixing 4 or 5 similar elements at one atomic site. While the high entropy materials exhibit magnetic properties distinct from their parent compounds, they also share certain similarities. With these two materials, we demonstrate that both band topology and sharp magnetic transition can survive in the high entropy phases. The final chapter provides an outlook on both research areas of research. The findings presented in this dissertation not only enrich our comprehension of fundamental science but also lay the foundation for future potential technological applications in some areas, such as Terahertz communication/imaging and energy harvesting.