*****NON-TECHNICAL ABSTRACT***** This Faculty Early Career Award at New Jersey Institute of Technology (NJIT) focuses on integrating fundamental studies of multiferroics with the education of students at different levels. Multiferroics belong to a novel class of oxide materials, whose magnetic and electrical properties are interconnected and can influence each other at low temperatures. Recently these materials have attracted great interest within the condensed-matter community and beyond due to the recognized potentials of multiferroics for future multifunctional device applications including magnetically recorded computer memory, optical switches for communication, and mechanical actuators. A comprehensive theory of the mechanisms for multiferroic effects is still under development. The proposed experimental studies of the related atomic vibrations will contribute to an increased understanding of these effects. The studies will also help in the search for new multiferroics that may lead to future devices that can operate in weaker magnetic fields and at higher temperatures. A diverse curriculum will be developed to promote the integration of modern materials research and education. Several Physics courses at NJIT, e.g. "Fundamental of Spectroscopy" and "Advanced Physics Laboratory", are to be directly associated with the proposed research. A comprehensive online course of Introductory Physics will be created for freshman students and will be used in outreach programs to local high-school students.
This Faculty Early Career Award at New Jersey Institute of Technology (NJIT) focuses on the integration of fundamental optical spectroscopy of the soft modes in multiferroic materials with education of students at different levels. Multiferroic magnetoelectrics belong to a novel class of ferroic oxides, whose magnetization and electrical polarization are closely coupled and can influence each other. By applying an electric field one can change the magnetization M in these crystals, while an external magnetic field affects the polarization P. A theoretical understanding of the P-M coupling at the crystal lattice level does not currently exist. The proposed experiments will use far-infrared spectroscopy at the National Synchrotron Light Source and Raman scattering, both in a magnetic field, to focus on this issue. The major research goal is to relate the interplay between anomalies in the dielectric function and magnetization of multiferroic single crystals to the behavior of the soft mode phonons, magnons, and crystal-field infrared-active excitations. Collaboration with National synchrotron radiation facilities is a key part of this project. Several Physics courses will be directly associated with the proposed research: "Fundamental of Spectroscopy" for graduate students and "Advanced Physics Laboratory" for fourth-year undergraduates. A comprehensive online course of Introductory Physics as well as a web-based interactive tool "Prepare for the Coming Quiz" will be created for freshman students and will be used in outreach programs to local high-school students.
Multiferroics are materials that possess both ferroelectric and ferromagnetic orderings. The ferroelectric effects are usually related to the crystal lattice distortions while ferromagnetism originates from the magnetic ion spins. Multiferroic effects open up an entirely new field of materials science with the potential for device applications in magnetic field sensors, optical switches for the THz spectral range, and digital data recording. Recently, a number of novel multiferroic materials with highly-non-linear and large magnetoelectric effects, such as the flipping of electric polarization, huge changes of the dielectric constant with applied magnetic fields, or large magnetization changes induced by applying electric fields, have been reported in literature. In spite of the remarkable progress in the field of multiferroics, the mechanisms of multiferroicity have not been well understood. The main goal of this Project was to contribute to a better understanding of multiferroic effects on a microscopic level by focusing our attention on infrared light propagation in multiferroics. This approach allowed us to investigate several important dynamic phenomena, which included the soft phonon modes that are related to the atomic vibrations and the coupling between these phonon modes with magnons, or magnetic dipoles, that are related to the spin dynamics. An extensive program of optical experiments was performed at the National Synchrotron Light Source at Brookhaven National Laboratory. Transmission of synchrotron radiation through thin slabs of several multiferroics has been studied at low temperatures and in strong external magnetic fields in the vicinity of the phase transitions in the investigated materials. Spectra of magnons, phonons, and crystal field excitations have been studied in several multiferroics materials including HoMn2O5, Tb3Fe5O12, and Dy3Fe5O12. A strong connection between the dynamic far-IR spectra and the unusual static dielectric and magnetic properties of multiferroic materials has been found. Results for HoMn2O5, Tb3Fe5O12, and Dy3Fe5O12 were published in research articles in the Physical Review B journal. During the course of the experimental studies of the light propagation in multiferroics, we found that optical transmission or reflection measurements alone cannot always distinguish between magnetic and electric dipoles, such as crystal field excitations, magnons, and phonons, and their electric- and magnetic-dipole oscillator strength cannot be determined due to fundamental limitations. To overcome this conceptual issue, we have developed a numeric method that allows for exact simulations of the optical data for Muller matrix, reflectivity, and transmission spectra of multiferroic materials, which are considered to be bi-anisotropic in our simulations. We published a LabVIEW-based tool online for the advanced optical spectra simulations, which is available to the entire Optical Community as a free download. PI was an Adviser for four Graduate Students at NJIT who were working on this Project. Two of them earned PhD Degrees in 2010 and 2011. One of the Students participated in a two-year long Outreach Program at one of the local High Schools in Newark. Immediately after graduation, this Graduate Student became a Faculty Member at the Physics Department of Rutgers University, Camden, at the rank of Assistant Professor. Another PhD Student returned to his prior field and he is now working as a Managing Director at one of the Capital Investment Companies in New York City. Two other Graduate Students passed their qualifiers and their graduation is expected in the near future. Four Undergraduate Students were supported by this Project. All of them were eventually admitted to Graduate Programs at Virginia Tech, Georgia Tech, and NJIT. One Postdoc was supported in this Project for 1 year. He attained a Research Professor position in Seoul National University. The PI of this Project developed three new Courses at NJIT for Undergraduate and Graduate Students: Phys450: Advanced Physics Lab, Phys446: Solid State Physics with concentration in Optics, and Phys774: Fundamentals of Spectroscopy.
