Active Multiferroic Nanostructures
This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 05-610, category NIRT. The objective of this research is to study magneto-electric interaction in nanoscale structures and facilitate the development of novel sensor and information storage devices. The approach is to design, model and synthesize artificial magneto-electric composites in the form of laminates, nanowires, and nanopillars. Mechanically coupled piezoelectric and magnetostrictive materials can artificially mimic the properties of true magneto-electric materials. The proposed research combines specific expertise in the field of molecular beam epitaxy, atomic layer epitaxy, laser assisted epitaxy, density functional theory and microwave magnetoelectrics into a synergistic program for: (a) epitaxial growth of active magneto-electric thin film/nanostructured layers, (b) density functional theory modeling of mechanically coupled nanostructured magneto-electric layers, and (c) fabrication and characterization of microwave magneto-electric test devices.
The proposed study will provide a science base for the development of miniature, passive (long-term deployable with batteries), ambient temperature operated (no need of cryostats), highly-sensitive (pico-Tesla), broad band (milli-Hz) systems with the nanostructured magneto-electric composites. Such devices are expected to offer new capabilities in biomedical sensing, microwave circuits, memory elements etc. Strong scientific capabilities in the area of these novel devices will facilitate rapid technological development in the United States. The commercial use of the above mentioned high performance nanostructure based magneto-electric devices will be beneficial for gas, bio-medical sensing as well as for passive microwave circuits for use in devices such as cell phones etc. The NIRT research team will coordinate and expand the existing education and outreach activities of the individual investigators into a cohesive and wide-ranging program. Existing sites on research experiences for undergraduates and teachers will be supplemented under the NIRT program to educate students and teachers in the area of multiferroics and novel nanostructures.
FOR AWARD # 0609377 NIRT: Active Multiferroic Nanostructures PI: Christos G. Takoudis University of Illinois Chicago September 16, 2011 Single phase multiferroics exhibit simultaneous ferroelectric and magnetic ordering in the same material system. As a result, they have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often there is some coupling between the two. Multiferroic materials are potentially advantageous for device miniaturization and can lead to additional functionalities, so that a single device component can perform more than one task. However, attempts to design multiferroics that combine ferromagnetism and ferroelectricity in the same phase have proved unexpectedly difficult, because the usual atomic-level mechanisms driving ferromagnetism and ferroelectricity are mutually exclusive. Although a few single phase multiferroic materials have been discovered by exploiting alternative mechanisms that lead to ferroelectricity or magnetism, none of them have proven suitable thus far for practical applications because of the very weak electric and magnetic polarization and cross coupling at room temperature. The synthesis, characterization and properties of novel perovskite-based oxide thin films and heterostructures using the pulsed laser deposition and atomic layer deposition techniques has been one of the main thrusts and contributions of the project. Besides targeting to achieve robust multiferroic properties in these complex oxides, the focus of the work has been on understanding the growth, structure-property relationships, physics of the materials, and controlled tuning of their properties. Related activities included (i) growth and structural characterization of double-perovskite thin films and heterostructures, and measurements of their magnetic electrical and magnetoelectric properties, and (ii) growth and characterization of multiferroic BiFeO3 thin films, including stabilization of a near-tetragonal phase on LaAlO3 substrate due to epitaxial strain. Composites are of interest for obtaining materials with desired properties for useful technologies. The primary objective of the research was to synthesize and characterize nano composites of magnetic and dielectric oxides. Such composites are capable of converting magnetic field to an electric field or vice versa. The field conversion occurs through mechanical strain generated in a magnetic or electric field. The approach was to prepare nano bilayers, nanowires and nanotubes of ferroelectric materials, such as lead zirconium titanante or barium titanate and ferromagnetic nickel- or cobalt ferrite. Significant contributions were on theoretical models for low-frequency and resonance magnetoelectric interactions in the nanocomposites. The theory predicts a giant low-frequency magneto-electric (ME) effect in nano pillars and nanowires of nickel ferrite (NFO) and lead zirconate titanate (PZT). The ME coupling is expected to be weak in bilayers on substrates due to substrate clamping. For wires of NFO and PZT on MgO template, the substrate pinning effects is negligible only when the wire radius is much greater than the sheath radius. The ME interactions were found to be the strongest for field orientations corresponding to minimum demagnetizing fields. The ME coupling at electromechanical and magneto-acoustic resonance are predicted to be strong in the nano composites and occurs at kHz to GHz frequencies, depending on the nature and dimensions of the nanocomposites. We identified for the first time a unique kind of phase boundary -- a so-called morphotropic phase boundary -- in BiFeO3, a material that is simultaneously ferroelectric and magnetic. The boundary is of fundamental scientific interest, because it is the first time that such a boundary has been discovered in a system consisting of a single material. Usually such boundaries are induced by tuning the phase behavior by alloying; in this case it was accessed using strain. It is also of potential technological value, because its occurrence in a multiferroic (magnetic and ferroelectric) material opens up the possibility of electric-field control of magnetism. Impacts - New materials for Consumer Electronics and the National Defense Three patents and one patent application on the nano-fabrication and potential use of composites in sensors and microwave devices were granted during 2007-2011. The universities involved intend to license the technology. Research Experiences for High School Students Ten high school interns were recruited from local high schools for research training. Their projects on nano-composite fabrication, sensors, miniature antennas and smart materials for energy harvesting resulted in several reports for the Siemens competition, Intel Science Talent Search, and Illinois Math and Science Academy.
