Gavin Lawes - US grants

Non-Technical Abstract
Materials that have simultaneous magnetic dipole and electric dipole order, called multiferroics, offer the potential for developing entirely new types of technological applications. Next generation multiferroic devices, including low-power/high-speed voltage switchable magnetic memory, may eventually replace current technologies for specific applications. However, before these concepts can be translated into real devices, it is necessary to understand the mechanisms giving rise to multiferroic order. The goal of this Faculty Early Career Development (CAREER) project at Wayne State University is to explain how magnetic and ferroelectric order can arise simultaneously at a single temperature. This project will investigate how ordered magnetic and electric dipoles interact in multiferroics under applied electric and magnetic fields using laser light and neutron scattering, among other techniques. These studies will help to explain how the magnetic and electric dipoles commun icate with one another in multiferroics, which will be crucial for designing better materials for innovative devices. This project will provide a platform for training the next generation of scientists through direct participation of graduate, undergraduate, and high school students in materials science research. Highlights from this exciting area of research will be incorporated into special topics lectures and demonstrations for Detroit area high school students.

Technical Abstract
This Faculty Early Career Development (CAREER) project at Wayne State University will investigate the simultaneous development of magnetic and ferroelectric order at a single phase transition in specific multiferroic oxides. The interplay between magnetic and ferroelectric degrees of freedom in these materials offers an extraordinary opportunity to study spin-charge coupling in "soft" materials that exhibit dramatic changes in their physical properties under externally applied fields. This project will explore the microscopic mechanisms for magnetoelectric couplings in multiferroics by studying low energy excitations under applied electric and magnetic fields using a variety of techniques including Raman and optical spectroscopy, neutron scattering, and thermodynamic characterization. Multiferroic thin film samples will be synthesized to investigate how a restricted geometry affects multiferroic order. This project will provide a platform for training the next generation of scientists through direct participation of graduate, undergraduate, and high school students in materials science research. Highlights from this exciting area of research will be incorporated into special topics lectures and demonstrations for Detroit area high school students.

Abstract

This instrument development project by a multi-disciplinary team from Wayne State University creates a Rapid Annealing and Characterization System (RACS) capable of rapidly annealing thin film samples and nanomaterials prepared externally and then characterizing these samples in situ using a variety of non-invasive techniques. With this highly flexible system, the researchers will develop and improve techniques to characterize how a variety of defects modify the materials properties. Defects, including dislocations, grain boundaries, impurity dopants, and vacancies have been found to dramatically alter the magnetic, electrical, and optical properties of materials. These defects are important in establishing the properties of nanomaterials, owing to the much higher surface to volume ratio than in bulk systems. The eventual goal of this study, which will focus on nitrides and superconducting thin films, is to control the type, density, and the distribution of defects to enable the synthesis of materials having specifically tailored properties. The custom designed vacuum chamber with rapid annealing capabilities coupled to a Scanning Electron Microscope with Wave Dispersion Spectrometer (WDS) using a proprietary airlock developed by JEOL will allow researchers to modify the defect structure by thermal annealing in one chamber and then conduct studies on the materials properties and defect structure in the second chamber, all without exposing the samples to ambient conditions. The WDS spectrometer is an important component of this study, as it will allow researchers to determine the concentration of oxygen vacancies, which is exceedingly difficult to determine using other techniques. The unique capabilities of RACS will be utilized to systematically probe the effects of a variety of defects on the fundamental properties of nanoscale systems, leading to a deeper understanding of how to tune the materials properties in nanostructured materials. Establishing the processing parameters for optimizing materials properties using RACS would allow the development of scalable fabrication protocols, which would promote the incorporation of these novel nanostructured materials into commercial devices. The development of this system will provide valuable training for a postdoctoral researcher as well as graduate and undergraduate students, specifically including underrepresented minorities in the Detroit metropolitan area.

****NON-TECHNICAL ABSTRACT****
Magnetism is one of the oldest phenomena known to men, yet one of the most difficult to understand. Magnetic materials, typically made from metallic ions such as nickel or cobalt, have been known and used for centuries. This project will pursue a series of experiments to test whether magnetism can arise in materials where none of the constituents are magnetic by themselves. This goal will be pursued by modifying oxygen-based semiconductors through the introduction of atomic scale point defects, specifically making holes in the ordered network of oxygen atoms. These defects are expected to lead to an increase in the electrical conductivity of these oxide semiconductors, which can trigger the development of ferromagnetism. A combination of imaging and analytical techniques, the interplay among mobile electrons, electrical gating, and optical excitations, will be used to elucidate how magnetism develops in these semiconducting systems. This award will substantially advance the fundamental understanding of how ferromagnetism develops in materials that are intermediate between metals and insulators as well as provide important insight into materials for making new magnetic memory and logic devices, which could be used for advanced computing. The students participating in this project will be trained in advanced analytical techniques applicable to careers in the semiconductor/nanotechnology industries, as well as in academia.

****TECHNICAL ABSTRACT****
This project will pursue a series of experiments to test a number of mechanisms that have been proposed for the development of room temperature ferromagnetism in semiconducting transition metal oxides, rationalizing the properties of materials intermediate between local moment magnetism and itinerant magnetism. These properties include the interplay between localized moments, mobile charge carriers, and point defects, specifically oxygen vacancies. This will be accomplished by correlating the emergence of an increased electrical conductivity in oxygen deficient oxide semiconductors with the development of ferromagnetism. Using a unique combination of imaging and analytical techniques it is expected to be possible to elucidate how the shift in carrier concentration with the inclusion of non-magnetic ions and point defects, electrical gating, and optical excitations affects these magnetic properties and how local moments from transition metals interact with the oxygen vacancy to induce ferromagnetism. This award will substantially advance the fundamental understanding of ferromagnetism by probing in a controlled manner the magnetism in systems intermediate between insulators and conductors. The two Ph.D. students and multiple undergraduates participating in this project will be trained in advanced analytical techniques applicable to careers in the semiconductor/nanotechnology industries, as well as in academia.

****Technical Abstract****
The goal of this project is to explore the physical basis for the concurrent magnetic and ferroelectric order that arises in multiferroic materials. The development of multiferroic order in materials is typically very tightly constrained by the symmetry of the lattice, which determines the transformation properties of the magnetic structure and the associated ferroelectric order. However, in low-symmetry crystals, the relative directions of the magnetic and ferroelectric structures are not restricted by symmetry, and expected to be determined only by the microscopic interactions. This project will focus on probing the microscopic interactions in multiferroics by studying the magnetic and ferroelectric order in iron vanadate, which is a low-symmetry material. These studies will use thermodynamic, magnetic, and electrical techniques to characterize the properties of iron vanadate samples, specifically the details of the magnetoelectric coupling. The microscopic interactions will be tuned by substitutional doping. This project will support the education and training of a PhD student, along with a number of undergraduate and high school studies. These students will be trained in a range of materials science techniques, including sample preparation, and sample characterization at low temperatures. Beyond the specialized training for these students, this project also included outreach efforts to introduce area high school students to current physics research topics as well as contributions to the development of a new Master's program in materials science.

****Non-Technical Abstract****
Materials having magnetic properties, such has conventional disk drives, and materials having electrical properties, such as transistors, both have integral roles in modern electronic devices. Recently, researchers have identified a new class of materials that have both magnetic properties and a special kind of electrical property called ferroelectricity. These materials, called multiferroics, offer the potential for developing entirely new types of electronic devices, like magnetic storage that can be controlled using voltage pulses, or non-volatile computer memory that will maintain information even with the power switched off. This project will investigate how these simultaneous magnetic and electrical properties develop in a specific iron-based multiferroic. This will be accomplished using thermodynamic, magnetic, and electrical measurements, all at very low temperatures, with additional detail on the magnetic properties provided by neutron scattering studies. This project will clarify how these joint magnetic and electrical properties can be controlled, with the goal of eventually designing materials that can be incorporated into consumer devices. Along with furthering our basic understanding of these multiferroic materials, this project will provide important training for students. One PhD graduate student, three undergraduate students, and three high school students will learn about preparing materials and electrical and magnetic studies at low temperature. This project will provide a strong background for these students as they prepare for careers in advanced scientific research and technology development.