RUI: EuO Thin Films as a Laboratory for Exploring Metal-Insulator Transitions and Colossal Magnetoresistance

Carleton College, Northfield MN

Investigators

Abstract

Non-technical abstract: In correlated electron materials, a phenomenon known as phase inhomogeneity is thought to be critical for explaining many interesting properties of these materials. This work will explore two physical phenomena that have been exhibited in correlated electron materials known as manganites: a metal-insulator transition associated with magnetic ordering and colossal magnetoresistance. This project will employ the binary compound Eu-rich EuO as a simplified system for studying the metal-insulator transition and colossal magnetoresistance. This project will fully characterize the metal-insulator transition in the EuO system, as well as searching for evidence of phase inhomogeneity in Eu-rich EuO. Exploration of the similarities of the Eu-rich EuO system to other correlated electron systems can enhance understanding of the mechanisms that are responsible for the properties of these materials. Understanding the nature of electronic, magnetic, and structural interactions that give rise to interesting phenomena, like the metal-insulator transition or colossal magnetoresistance, in the long run may provide insights as to how to take advantage of these materials for applications such as sensors or electronic devices. Additionally, this work will help meet the growing demand for a technical workforce by training undergraduates in experimental techniques, including sample growth and physical properties measurements. Technical abstract: Phase inhomogeneity has emerged as a significant paradigm for describing a wide range of correlated electron materials, including the colossal magnetoresistive manganites. Like the manganites, Eu-rich EuO exhibits colossal magnetoresistance and ferromagnetic ordering at low temperatures with an accompanying insulator-metal transition. However, Eu-rich EuO provides a simplified laboratory for exploring the metal-insulator transition and colossal magnetoresistance because of its reduced structural complexity as compared to the manganites. This single investigator award will support an experimental study of Eu-rich EuO thin films with the objective of characterizing the transport and magnetotransport properties in light of the theoretical Kondo-lattice model that has been developed to describe the metal-insulator transition and colossal magnetoresistance of the EuO system. To explore the metal-insulator transition, the resistivity of the Eu-rich EuO films will be modulated both by controlling the oxygen deficiency of the samples and by controlling the carrier density via the electric field effect. Additionally, the supported work will look for indirect signatures of phase inhomogeneity in the magnetization and transport behavior of the Eu-rich EuO thin films, providing additional insight into role of phase inhomogeneity in determining material properties. This project will also train undergraduates in experimental techniques, including sample growth and transport and magnetization measurements, thereby helping to develop future physicists.