Browsing by Author "Lee, S."

Now showing 1 - 3 of 3

Correlation between nanoscale and nanosecond resolved ferroelectric domain dynamics and local mechanical compliance
(2011-05-01)
Polomoff, N. A.
;
Rakin, A.
;
Lee, S.
;
Palumbo, V.
;
Yu, P.
The local dynamics of ferroelectric domain polarization are uniquely investigated with sub-20-nm resolved maps of switching times, growth velocities, and growth directions. This is achieved by analyzing movies of hundreds of consecutive high speed piezo force microscopy images, which record domain switching dynamics through repeatedly alternating between high speed domain imaging and the application of 20-nanosecond voltage pulses. Recurrent switching patterns are revealed, and domain wall velocities for nascent domains are uniquely reported to be up to four times faster than for mature domains with radii greater than approximately 100 nm. Switching times, speeds, and directions are also shown to correlate with local mechanical compliance, with domains preferentially nucleating and growing in compliant sample regions while clearly shunting around locations with higher stiffness. This deterministic switching behavior strongly supports a defect-mediated energy landscape which controls polarization reversal, and that can therefore be predicted, modeled, and even manipulated through composition, processing, and geometry. Such results have important implications for the practical performance of ferroelectric devices by enabling guided optimization of switching times and feature densities, while the methods employed provide a new means to investigate and correlate dynamic functionality with mechanical properties at the nanoscale. (C) 2011 American Institute of Physics. [doi:10.1063/1.3581205]
Optical properties and magnetochromism in multiferroic BiFeO(3)
(2009-04-01)
Xu, X. S.
;
Brinzari, T. V.
;
Lee, S.
;
Chu, Y. H.
;
Martin, L. W.
In order to investigate spin-charge coupling in multiferroic oxides, we measured the optical properties of BiFeO(3). Although the direct 300 K charge gap is observed at 2.67 eV, absorption onset actually occurs at much lower energy with Fe(3+) excitations at 1.41 and 1.90 eV. Temperature and magnetic-field-induced spectral changes reveal complex interactions between on-site crystal-field and magnetic excitations in the form of magnon sidebands. We employ the sensitivity of these magnon sidebands to map out the magnetic-field-temperature phase diagram which demonstrates optical evidence for spin spiral quenching above 20 T and suggests a spin domain reorientation near 10 T.
Optical properties and magnetochromism in multiferroic BiFeO3
(2009-04-01)
Xu, X. S.
;
Brinzari, T. V.
;
Lee, S.
;
Chu, Y. H.
;
Martin, L. W.
In order to investigate spin-charge coupling in multiferroic oxides, we measured the optical properties of BiFeO3. Although the direct 300 K charge gap is observed at 2.67 eV, absorption onset actually occurs at much lower energy with Fe3+ excitations at 1.41 and 1.90 eV. Temperature and magnetic-field-induced spectral changes reveal complex interactions between on-site crystal-field and magnetic excitations in the form of magnon sidebands. We employ the sensitivity of these magnon sidebands to map out the magnetic-field-temperature phase diagram which demonstrates optical evidence for spin spiral quenching above 20 T and suggests a spin domain reorientation near 10 T.