FY2010 - Oak Ridge National Laboratory

Seed Money Fund—
Materials Science and Technology Division
Advanced Research Projects Agency, since the oxide-based field effect transistors are very promising for
many technical applications such as sensors, energy and information storage, and piezoelectric devices.
Results and Accomplishments
High-quality ferroelectric thin films in field-effect transistor (FET) structures play a key role. Thus,
epitaxial synthesis of CEO/ferroelectric bilayers on conducting substrates has been conducted. By using
such samples, this research has enabled the successful demonstration of high on/off switching ratio for the
first time. A clear metal-insulator transition is observed with a drastic change in resistivity by changing
the polarization direction. A dramatically high switching ratio (ΔR/R = 100,000%) has been obtained in
(La 1-x Sr x )MnO 3 (x = 0.2 and 0.5) films. This is a drastic improvement over the previously reported best
record value of 20%. Comparing it with electronic transport we speculate that the charge carrier mobility
is modified by the creation of a very clean, highly conductive LSMO/PZT interface due to the
ferroelectric field effect. In case of magnetism, while we have observed only a small change in total
magnetization between two polarization-switching states, the systematic change in Tc has been found,
confirming the change in Tc found from the DC transport measurement. We envision that the successful
completion of this project will have a big impact on the study of nonvolatile information storage devices
and on attracting future funding. Currently, testing our prototype transistors is under discussion with a
semiconductor memory company.
05856
Spin Excitations and Multiferroic State of Doped CuFeO 2
Randy Fishman, Feng Ye, and Jaime Fernandez-Baca
Project Description
Due to the strong coupling between the electric polarization and the magnetization, multiferroic materials
hold tremendous technological promise in the magnetic storage industry based on the ability to
manipulate magnetic bits with electric currents. This project utilizes ORNL’s unique strengths in
computation, theory, and neutron sciences by combining theoretical modeling with elastic and inelastic
neutron-scattering measurements to study the multiferroic phase of a typical ferroelectric material.
Comparing the observed spin excitations with theoretical predictions will allow us to characterize the
multiferroic state and the microscopic interactions responsible for the ferroelectric behavior. This project
will demonstrate that, because of the unique coupling between the neutron and electron spins, neutron
scattering provides an indispensible tool in the search for new multiferroic materials. The successful
completion of this project will lay the foundation for a combined modeling and neutron-based program on
multiferroic materials that will attract funding from both scientific and user-based agencies.
Mission Relevance
This research bears directly on the strengths at ORNL in computation and neutron sciences. As a national
center for neutron scattering, ORNL can make an immediate impact in the experimental characterization
of multiferroic behavior.
Results and Accomplishments
We have evaluated the magnetic ground state and spin dynamics of a gallium-doped CuFeO 2 compound
(3.5% gallium doping) in its multiferroic phase. We also measured the excitation spectrum of this
material using the neutron-scattering facilities at ORNL. This work was published in a Rapid
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