Browsing by Author "Nagarajan, Valanoor"

Now showing 1 - 9 of 9

Deterministic optical control of room temperature multiferroicity in BiFeO3 thin films
(2019-06-01)
Liou, Yi-De
;
Chiu, Yu-You
;
Hart, Ryan Thomas
;
Kuo, Chang-Yang
;
Huang, Yen-Lin
Controlling ferroic orders (ferroelectricity, ferromagnetism and ferroelasticity) by optical methods is a significant challenge due to the large mismatch in energy scales between the order parameter coupling strengths and the incident photons. Here, we demonstrate an approach to manipulate multiple ferroic orders in an epitaxial mixed-phase BiFeO3 thin film at ambient temperature via laser illumination. Phase-field simulations indicate that a light-driven flexoelectric effect allows the targeted formation of ordered domains. We also achieved precise sequential laser writing and erasure of different domain patterns, which demonstrates a deterministic optical control of multiferroicity at room temperature. As ferroic orders directly influence susceptibility and conductivity in complex materials, our results not only shed light on the optical control of multiple functionalities, but also suggest possible developments for optoelectronics and related applications.
Electrical Control of Multiferroic Orderings in Mixed-Phase BiFeO3 Films
(2012-06-12)
Chen, Yi-Chun
;
He, Qing
;
Chu, Feng-Nan
;
Huang, Yen-Chin
;
Chen, Jhih-Wei
Epitaxial NiO nanocrystals: a dimensional analysis
(2013-06-01)
Cheung, Jeffrey
;
Okatan, Mahmut Baris
;
Sullaphen, Jivika
;
Cheng, Xuan
;
Nagarajan, Valanoor
We present the study of the synthesis of (001) nickel oxide (NiO) epitaxial nanocrystals grown on (001) strontium titanate (SrTiO3) single crystal substrates. Pulsed laser deposition of the bismuth nickel oxide (BiNiO3, BNO) perovskite precursor followed by post-deposition processing is carried out to form the NiO nanocrystals. A detailed analysis of the dimensions of nanocrystals reveals that the morphology attained differs from the thermodynamically expected equilibrium shape. The deviations from the equilibrium shape are found to follow a systematic trend where the in-plane basal dimensions, that is, the length and width of the nanocrystals grown differ in discretized dimensions. This discretization suggests that for a given interfacial area of nanocrystals there are multiple stable basal rectangular geometries attainable.
Exploring Topological Defects in Epitaxial BiFeO(3) Thin Films
(2011-02-01)
Vasudevan, Rama K.
;
Chen, Yi-Chun
;
Tai, Hsiang-Hua
;
Balke, Nina
;
Wu, Pingping
Using a combination of piezoresponse force microscopy (PFM) and phase-field modeling, we demonstrate ubiquitous formation of center-type and possible ferroelectric closure domain arrangements during polarization switching near the ferroelastic domain walls in (100) oriented rhombohedral BiFeO(3). The formation of these topological defects is determined from the vertical and lateral PFM data and confirmed from the reversible changes in surface topography. These observations provide insight into the mechanisms of tip-induced ferroelastic domain control and suggest that formation of topological defect states under the action of local defect- and tip-induced fields is much more common than previously believed.
Exploring Topological Defects in Epitaxial BiFeO3 Thin Films
(2011-02-01)
Vasudevan, Rama K.
;
Chen, Yi-Chun
;
Tai, Hsiang-Hua
;
Balke, Nina
;
Wu, Pingping
Using a combination of piezoresponse force microscopy (PFM) and phase-field modeling, we demonstrate ubiquitous formation of center-type and possible ferroelectric closure domain arrangements during polarization switching near the ferroelastic domain walls in (100) oriented rhombohedral BiFeO3. The formation of these topological defects is determined from the vertical and lateral PFM data and confirmed from the reversible changes in surface topography. These observations provide insight into the mechanisms of tip-induced ferroelastic domain control and suggest that formation of topological defect states under the action of local defect- and tip-induced fields is much more common than previously believed.
Nanoscale Control of Phase Variants in Strain-Engineered BiFeO(3)
(2011-08-01)
Vasudevan, Rama K.
;
Liu, Yunya
;
Li, Jiangyu
;
Liang, Wen-I
;
Kumar, Amit
Development of magnetoelectric, electromechanical, and photovoltaic devices based on mixed-phase rhombohedral-tetragonal (R-T) BiFeO(3) (BFO) systems is possible only if the control of the engineered R phase variants is realized. Accordingly, we explore the mechanism of a bias induced phase transformation in this system. Single point spectroscopy demonstrates that the T -> R transition is activated at lower voltages compared to T -> - T polarization switching. With phase field modeling, the transition is shown to be electrically driven. We further demonstrate that symmetry of formed R-phase rosettes can be broken by a proximal probe motion, allowing controlled creation of R variants with defined orientation. This approach opens a pathway to designing next-generation magnetoelectronic and data storage devices in the nanoscale.
Nanoscale Control of Phase Variants in Strain-Engineered BiFeO3
(2011-08-01)
Vasudevan, Rama K.
;
Liu, Yunya
;
Li, Jiangyu
;
Liang, Wen-I
;
Kumar, Amit
Development of magnetoelectric, electromechanical, and photovoltaic devices based on mixed-phase rhombohedral-tetragonal (R-T) BiFeO3 (BFO) systems is possible only if the control of the engineered R phase variants is realized. Accordingly, we explore the mechanism of a bias induced phase transformation in this system. Single point spectroscopy demonstrates that the T -> R transition is activated at lower voltages compared to T -> - T polarization switching. With phase field modeling, the transition is shown to be electrically driven. We further demonstrate that symmetry of formed R-phase rosettes can be broken by a proximal probe motion, allowing controlled creation of R variants with defined orientation. This approach opens a pathway to designing next-generation magnetoelectronic and data storage devices in the nanoscale.
Self-Assembled Epitaxial Core-Shell Nanocrystals with Tunable Magnetic Anisotropy
(2015-09-02)
Liao, Sheng-Chieh
;
Chen, Yong-Lun
;
Kuo, Wei-Cheng
;
Cheung, Jeffrey
;
Wang, Wei-Cheng
Synthesis of Epitaxial Metal Oxide Nanocrystals via a Phase Separation Approach
(2010-09-01)
Bogle, Kashinath A.
;
Anbusathaiah, Varatharajan
;
Arredondo, Miryam
;
Lin, Jiunn-Yuan
;
Chu, Ying-Hao
Perovskite phase instability of BiMnO(3) has been exploited to synthesize epitaxial metal oxide magnetic nanocrystals. Thin film processing conditions are tuned to promote the breakdown of the perovskite precursor into Bi(2)O(3) matrix and magnetic manganese oxide islands. Subsequent cooling in vacuum ensures complete volatization of the Bi(2)O(3), thus leaving behind an array of self-assembled magnetic Mn(3)O(4) nanostructures. Both shape and size can be systematically controlled by the ambient oxygen environments and deposition time. As such, this approach can be extended to any other Bi-based complex ternary oxide system as it primarily hinges on the breakdown of parent Bi-based precursor and subsequent Bi(2)O(3) volatization.