CAREER: Hexagonal Ferrite Thin Films for the High-Temperature Magnetoelectric Memory Effect

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NON-TECHNICAL SUMMARYThe discovery and utilization of the dynamic coupling between the electric and magnetic fields - electromagnetic waves - has revolutionized human society, particularly in the wireless communications. The "static" couplings between the electric and magnetic fields in a material (e.g. switching the north and south poles of a magnet using an electric field) are expected to have major applications in compact and energy efficient information storage and processing, sensors, and actuators. These applications are desired since the demand for information storage and processing is ever increasing while the capabilities of current technology are being exhausted. This Faculty Early Career Development (CAREER) project explores the possible static couplings between the electric and magnetic fields in new materials, such as hexagonal ferrites, by elucidating the connections between their electric, magnetic, and structural properties, and fine-tuning the materials using advanced material preparations. Integrated with the research, the educational objectives of this project are, to promote teaching undergraduate students fundamental physics by exposing them to cutting-edge research and by exploiting new student-centered pedagogical approaches, to mentor and inspire student researchers with systematic trainings for innovative research, and to engage K-12 students to stimulate their interests in science.TECHNICAL SUMMARY Switching a magnetic dipole using an electric field (magnetoelectric memory effect) - an effect that can be a working principle of the next-generation technology for information processing and storage - is unfortunately rare in known materials and restricted to low temperature. This Faculty Early Career Development (CAREER) project explores the magnetoelectric memory effect that is efficient and stable at high temperature, by the discovery of new materials or by tuning the properties of known materials experimentally. In particular, this project investigates the possible magnetoelectric memory effect in the materials that exhibit both improper ferroelectricity and improper ferromagnetism, such as hexagonal ferrites (h-RFeO3; R =Y, Ho, Lu). The specific research objectives of the proposed work are: 1) Elucidate the origin of the magnetic orderings in hexagonal ferrites. 2) Experimentally determine the magnetoelectric effect and identify the underlying mechanism in hexagonal ferrites. 3) Adjust the magnetic properties and the coupling between the magnetic and electric properties in hexagonal ferrites by tuning their structures using epitaxial thin film growth. Pulsed laser deposition method is employed to prepare single crystalline epitaxial thin film materials of tuned structures. The details of magnetic, electronic, and lattice structures are investigated using neutron scattering, x-ray spectroscopy, and x-ray diffraction respectively. The couplings between the electric and magnetic properties are studied by measuring the change of ferromagnetic properties in an electric field. Besides advancing the understanding in the magnetoelectric couplings in complex oxides in general, the success of the project may experimentally establish a new paradigm of magnetoelectric effect originated from improper ferroelectricity and improper ferromagnetism