New Research Trends in Electrically Tunable 2D van der Waals Magnetic Materials

The recent discovery of two-dimensional (2D) van der Waals (vdW) magnetic materials has provided new, unprecedented opportunities for both fundamental science and technological applications. Unlike three-dimensional (3D) magnetic systems, the electric manipulation of vdW magnetism (e.g., magnetization state, magnetic anisotropy, magnetic ordering temperature) down to the monolayer limit at ambient conditions enables high efficiency operation and low energy consumption, which has the potential to revolutionize the fields of spintronics, spin-caloritronics, and valleytronics. This article provides an in-depth analysis of the recent progress, emerging opportunities, and technical challenges in the electric manipulation of magnetic functionalities of a wide variety of 2D vdW magnetic systems ranging from metals to semiconductors and heterostructures. The state-of-the-art understanding of the mechanisms behind the electric modulation of magnetism in these 2D vdW magnetic systems will drive future research towards novel applications in spintronics, spin-caloritronics, valleytronics, and quantum computation

Multi-Fields Modulation of Physical Properties of Oxide Thin Films

Oxide thin films exhibit versatile physical properties such as magnetism, ferroelectricity, piezoelectricity, metal-insulator transition (MIT), multiferroicity, colossal magnetoresistivity, switchable resistivity, etc. More importantly, the exhibited multifunctionality could be tuned by various external fields, which has enabled demonstration of novel electronic devices. In this article, recent studies of the multi-fields modulation of physical properties in oxide thin films have been reviewed. Some of the key issues and prospects about this field are also addressed.Comment: review article, 56 pages, 18 figure

Hybrid spintronic materials:Growth, structure and properties

10.1016/j.pmatsci.2018.08.001Progress in Materials Science9927-10

Gate-Tunable Magnetotransport in Ferromagnetic ZnO Nanowire FET Devices

Department of Materials Science EngineeringElectrical manipulation of magnetization has grown as an essential ingredient in rapidly evolving spintronic research. Switching of nano-scale magnetization can be induced by a spin-polarized current via spin-transfer torque, domain wall motion, and/or spin-orbit torque, which are being increasingly utilized for magnetic memory devices under development. Apart from current dissipation, the electric field itself can also be used to control the magnetism in various materials, especially in dilute magnetic semiconductors (DMSs). A gate-voltage-induced accumulation of charge could alter magnetic exchange interactions and eventually lead to changes in magnetic moment, coercivity, anisotropy, and transition temperature. Semiconductor spintronics has garnered increasing attention due to the concept behind the spin field-effect transistor (spin-FET), where the spin precession is governed by the gate-controllable Rashba field. Tuning the magnetization of the source and drain in the spin-FET architecture offers additional state variables in future state-of-the-art electronic applications. This dissertation addresses the study of dramatic gate-induced change of ferromagnetism in ZnO nanowire (NW) field-effect transistors (FETs). The ZnO NWs used in this study were grown by using chemical vapor deposition (CVD) technique. The crystal structure and composition of ZnO NWs were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). Ferromagnetism in our ZnO NWs arose from oxygen vacancies, which constitute deep levels hosting unpaired electron spins. The magnetic transition temperature of the studied ZnO NWs was estimated to be well above room temperature. The in situ UV confocal photoluminescence (PL) study confirmed oxygen vacancy mediated ferromagnetism in the studied ZnO NW FET devices. Both the estimated carrier concentration and temperature dependent conductivity reveal the studied ZnO NWs are at the crossover of the metal-insulator transition. In particular, gate-induced modulation of the carrier concentration in the ZnO NW FET significantly alters carrier-mediated exchange interactions, which causes even inversion of magnetoresistance (MR) from negative to positive values. Upon sweeping the gate bias from −40 V to +50 V, the MRs estimated at 2 T and 2 K were changed from −11.3% to +4.1%. Detailed analysis on the gate dependent MR behavior clearly showed enhanced spin splitting energy with increasing carrier concentration. Gate voltage dependent PL spectra of an individual NW device confirmed the localization of oxygen vacancy-induced spins, indicating that gate-tunable indirect exchange coupling between localized magnetic moments played an important role in the remarkable change of the MR.ope

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Interaction between Charge-transfer States Studied by Magnetic Field Effects

Organic semiconducting materials, consisting mostly of carbon and hydrogen atoms, provide remarkable promise for electronic applications due to their easy processing, chemical tenability, low costs and environmental-friendly characteristics. For realizing electronic applications such as light emitting diodes and photovoltaic cells, charge-transfer states act as an important intermediate state for recombination and dissociation. Interestingly, magnetic field effects on semiconducting materials have been realized based on the suppression of spin mixing in the charge-transfer states. Although lots of studies have been carried out on investigating the properties of charge-transfer states, little has been done to consider the interaction between them. This thesis aims to reveal the interaction between different kinds of charge-transfer states by using the magnetic field effects. Chapter 1 presents a basic introduction to the organic semiconducting materials and magnetic field effects. Chapter 2 gives a simple description of the experiment procedure, such as device fabrication, magnetic field effects measurement and data analysis. Chapter 3 studies the interaction between intermolecular charge-transfer states. Chapter 4 indicates the interaction between intramolecular charge-transfer states and d electrons. Chapter 5 illustrates the interaction between photo-generated and magnetized charge-transfer states. Chapter 6 introduces the interaction between excitons and free charge carriers in organo-metal halide perovskite materials. Chapter 7 performs the study of magneto-electronic interaction at the interface between Rashba perovskite and ferromagnetic metal. Finally, Chapter 8 gives a short conclusion for the entire study in this dissertation