Browsing by Author "He, Qing"

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A Metal-Insulator Transition of the Buried MnO2 Monolayer in Complex Oxide Heterostructure
(2016-11-02)
Liu, Heng-Jui
;
Lin, Jheng-Cyuan
;
Fang, Yue-Wen
;
Wang, Jing-Ching
;
Huang, Bo-Chao
A novel artificially created MnO2 monolayer system is demonstrated in atomically controlled epitaxial perovskite heterostructures. With careful design of different electrostatic boundary conditions, a magnetic transition as well as a metal-insulator transition of the MnO2 monolayer is unveiled, providing a fundamental understanding of dimensionality-confined strongly correlated electron systems and a direction to design new electronic devices.
Anomalous Electronic Anisotropy Triggered by Ferroelastic Coupling in Multiferroic Heterostructures
(2016-02-03)
Ju, Changcheng
;
Yang, Jan-Chi
;
Luo, Cheng
;
Shafer, Padraic
;
Liu, Heng-Jui
Atomic-Scale Evolution of Local Electronic Structure Across Multiferroic Domain Walls
(2011-04-05)
Chiu, Ya-Ping
;
Chen, Yu-Ting
;
Huang, Bo-Chao
;
Shih, Min-Chuan
;
Yang, Jan-Chi
Direct evidence of the electronic configurations across domain walls in BiFeO(3) is quantitatively characterized by cross-sectional scanning tunneling microscopy. Atomic-scale band evolution and the asymmetrically built-in potential barrier at domain boundaries are demonstrated. The 109 degrees domain walls register a remarkable decrease in the bandgap, suggesting a new route to control the local conducting channels within 2 nm.
Atomic-Scale Visualization of Polarization Pinning and Relaxation at Coherent BiFeO3/LaAlO3 Interfaces
(2014-02-01)
Huang, Rong
;
Ding, Hang-Chen
;
Liang, Wen-I
;
Gao, Yong-Chao
;
Tang, Xiao-Dong
Complex oxide heterointerfaces, which play host to an incredible variety of interface physical phenomena, are of great current interest in introducing new functionalities to systems. Here, coherent super-tetragonal BiFeO3/LaAlO3 and rhombohedral BiFeO3/LaAlO3 heterointerfaces are investigated by using a combination of high-angle annular dark-field (HAADF) imaging and annular bright-field (ABF) imaging in a spherical aberration (Cs) corrected scanning transmission electron microscope (STEM), and first-principles calculations. The complicated ferroelectric polarization pinning and relaxation that occurs at both interfaces is revealed with atomic resolution, with a dramatic change in structure of BiFeO3, from cubic to super-tetragonal-like. The results enable a detailed explanation to be given of how non-bulk phase structures are stabilized in thin films of this material.
BiFeO3 Thin Films: A Playground for Exploring Electric-Field Control of Multifunctionalities
(2015-01-01)
Yang, Jan-Chi
;
He, Qing
;
Yu, Pu
;
Chu, Ying-Hao
;
材料科學與工程學系
A promising approach to the next generation of low-power, functional, and green nanoelectronics relies on advances in the electric-field control of lattice, charge, orbital, and spin degrees of freedom in novel materials. The possibility of electric-field control of these multiple materials functionalities offers interesting options across a range of modern technologies, including information communication, computing processes, data storage, active components, and functional electronics. This article reviews electric-field control and modulation of various degrees of freedom through the medium of multiferroic BiFeO3. Coexisting order parameters and inherent couplings in this materials system form a potent playground, enabling direct and indirect manipulation to obtain intriguing properties and functionalities with an electric stimulus. An in-depth understanding of those electrically controlled phenomena and breakthroughs is highlighted, paving a new route toward multifunctional nanoelectronics. This article concludes with a brief discussion on foreseeable challenges as well as future directions.
Concurrent transition of ferroelectric and magnetic ordering near room temperature
(2011-11-01)
Ko, Kyung-Tae
;
Jung, Min Hwa
;
He, Qing
;
Lee, Jin Hong
;
Woo, Chang Su
Strong spin-lattice coupling in condensed matter gives rise to intriguing physical phenomena such as colossal magnetoresistance and giant magnetoelectric effects. The phenomenological hallmark of such a strong spin-lattice coupling is the manifestation of a large anomaly in the crystal structure at the magnetic transition temperature. Here we report that the magnetic Neel temperature of the multiferroic compound BiFeO3 is suppressed to around room temperature by heteroepitaxial misfit strain. Remarkably, the ferroelectric state undergoes a first-order transition to another ferroelectric state simultaneously with the magnetic transition temperature. Our findings provide a unique example of a concurrent magnetic and ferroelectric transition at the same temperature among proper ferroelectrics, taking a step toward room temperature magnetoelectric applications.
Direct spectroscopic evidence of charge reversal at the Pb(Zr(0.2)Ti(0.8))O(3)/La(0.7)Sr(0.3)MnO(3) heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
;
Chen, Yi-Chun
;
Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr(0.2)Ti(0.8))O(3) (PZT) ultrathin film and a bottom La(0.7)Sr(0.3)MnO(3) (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Direct spectroscopic evidence of charge reversal at the Pb(Zr0.2Ti0.8)O-3/La0.7Sr0.3MnO3 heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
;
Chen, Yi-Chun
;
Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr0.2Ti0.8)O-3 (PZT) ultrathin film and a bottom La0.7Sr0.3MnO3 (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Directed assembly of nano-scale phase variants in highly strained BiFeO3 thin films
(2012-09-15)
Zhou, Jian
;
Trassin, Morgan
;
He, Qing
;
Tamura, Nobumichi
;
Kunz, Martin
The delicate balance between elastic energy and electrostatic energy in highly strained BiFeO3 (BFO) thin films results in complex mixed-phase patterns, which poses significant challenges for theoretical understanding and complicates the realization of its full potential in magnetoelectric, electromechanical, and photovoltaic devices. In this letter, we explore in-plane electric field induced phase transition in strain engineered BFO thin films and elucidate the mechanism behind the assembly behavior of complex nano-scale phase domains. Our approach enables deterministic control of phase variants with well-defined structures and orientation, paving the way for designing novel data storage devices based on mixed phase BFO. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752395]
Domain wall functionality in BiFeO3
(2013)
Seidel, Jan
;
Singh-Bhalla, Guneeta
;
He, Qing
;
Yang, Seung-Yeul
;
Chu, Ying-Hao
In this article we provide an overview of phenomena involving domain walls in BiFeO3 as nanoscale functional elements. Because ferroelectric domain walls can be routinely modified using electric fields, our results suggest a new degree of flexibility for domain boundary engineering and oxide-based nanoelectronics.
Electric Field Writing of Ferroelectric Nano-Domains Near 71 degrees Domain Walls with Switchable Interfacial Conductivity
(2018-08-01)
Yang, Shuzhen
;
Peng, Ren-Ci
;
He, Qing
;
Huang, Yen-Lin
;
Huang, Yijing
Conducting ferroelectric domain walls attract a wide range of research interest due to their promising applications in nanoelectronics. In this study, we reveal an unexpected enhanced conductivity near the well-aligned 71 degrees nonpolar domain walls in BiFeO3. Such an interfacial conductivity is induced by the creation of up-polarized nano-domains near the 71 degrees domain walls, as revealed by the combination of the piezo-response force microscopy (PFM) and conducting atomic force microscopy (c-AFM) imaging techniques, as well as phase-field simulations. The upward polarized domains are suggested to lower the Schottky barrier at the interface between the tip and sample surface, and then give rise to the enhanced interfacial conductivity. The result provides a new strategy to tune the local conductance in ferroelectric materials and opens up new opportunities to design novel nanoelectronic devices.
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
Electrically enhanced magnetization in highly strained BiFeO3 films
(2016-05)
Yang, Jan-Chi
;
Kuo, Chang-Yang
;
Liu, Heng-Jui
;
Ding, Hang-Chen
;
Duan, Chun-Gang
The control of magnetism via an electric field has attracted substantial attention because of potential applications in magnetoelectronics, spintronics and high-frequency devices. In this study, we demonstrate a new approach to enhance and control the magnetization of multiferroic thin film by an electric stimulus. First, to reduce the strength of the antiferromagnetic superexchange interaction in BiFeO3, we applied strain engineering to stabilize a highly strained phase. Second, the direction of the ferroelectric polarization was controlled by an electric field to enhance the Dzyaloshinskii-Moriya interaction in the highly strained BiFeO3 phase. Because of the magnetoelectric coupling in BiFeO3, a strong correlation between the modulated ferroelectricity and enhanced magnetization was observed. The tunability of this strong correlation by an electric field provides an intriguing route to control ferromagnetism in a single-phase multiferroic.
Enhanced Magnetocaloric Effect Driven by Interfacial Magnetic Coupling in Self-Assembled Mn3O4-La0.7Sr0.3MnO3 Nanocomposites
(2015-12-09)
Vandrangi, Suresh K.
;
Yang, Jan-Chi
;
Zhu, Yuan-Min
;
Chin, Yi-Ying
;
Lin, Hong-Ji
Magnetic refrigeration, resulting from the magneto caloric effect of a material around the magnetic phase-transition temperature, is a topic of great interest as it is considered to be an alternate energy solution to conventional vapor-compression refrigeration. The viability of a magnetic refrigeration system for magnetic cooling can be tested by exploiting materials in various forms, from bulk to nanostrucutres. In this study, magnetocaloric properties of self-assembled Mn3O4-La0.7Sr0.3MnO3 nanocomposites, with varying doping concentrations of Mn3O4 in the form of nanocrystals embedded in the La0.7Sr0.3MnO3 matrix, are investigated. The temperatures corresponding to the paramagnetic-to-ferromagnetic transitions are higher, and the values of change in magnetic entropy under a magnetic field of 2 T show an enhancement (highest being similar to 130%) for the nanocomposites with low doping concentrations of Mn3O4, compared to that of pure La0.7Sr0.3MnO3 thin films. Relative cooling power remain close to those of La0.7Sr0.3MnO3. The enhanced magnetic phase-transition temperature and magnetocaloric effect are interpreted and evidenced in the framework of interfacial coupling between Mn3O4 and La0.7Sr0.3MnO3. This work demonstrates the potentiality of self-assembled nanostructures for magnetic cooling near room temperature under low magnetic fields.
Enhanced Structural and Magnetic Coupling in a Mesocrystal-Assisted Nanocomposite
(2016-01-20)
Zhu, Yuanmin
;
Zhan, Qian
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Yang, Jan-Chi
;
Bitla, Yugandhar
;
Liu, Pingping
Benefiting from the advances made in well-controlled materials synthesis techniques, nanocomposites have drawn considerable attention due to their enthralling physics and functionalities. In this work, we report a new heteroepitaxial mesocrystalperovskite nanocomposite, (NiFe2O4)(0.33):(La0.67Ca0.33MnO3)(0.67). Elaborate structural studies revealed that tiny NiFe2O4 nanocrystals aggregate into ordered octahedral mesocrystal arrays with {111} facets together with a concomitant structural phase transition of the La0.67Ca0.33MnO3 matrix upon postannealing process. Combined magnetic and X-ray absorption spectroscopic measurements show significant enhancement in the magnetic properties at room temperature due to the structural evolution of magnetic NiFe2O4 and the consequent magnetic coupling at the heterointerfaces mediating via well connected octahedrons of Mn-O-6 in La0.67Ca0.33MnO3 and (Ni,Fe)-O-6 in NiFe2O4. This work demonstrates an approach to manipulate the exciting physical properties of material systems by integrating desired functionalities of the constituents via synthesis of a self-assembled mesocrystal embedded nanocomposite system.
Epitaxial Photostriction-Magnetostriction Coupled Self-Assembled Nanostructures
(2012-08-01)
Liu, Heng-Jui
;
Chen, Long-Yi
;
He, Qing
;
Liang, Chen-Wei
;
Chen, Yu-Ze
Self-assembled vertical nanostructures take advantage of high interface-to-volume ratio and can be used to design new functionalities by the choice of a proper combination of constituents. However, most of the studies to date have emphasized the functional controllability of the nanostructures using external electric or magnetic fields. In this study, to introduce light (or photons) as an external control parameter in a self-assembled nanostructure system, we have successfully synthesized oxide nanostructures with CoFe2O4 nanopillars embedded in a SrRuO3 matrix. The combination of photostrictive SrRuO3 and magnetostrictive CoFe2O4 in the intimately assembled nanostructures leads to a light-induced, ultrafast change in magnetization of the CoFe2O4 nanopillars. Our work demonstrates a novel concept on oxide nanostructure design and opens an alternative pathway for the explorations of diverse functionalities in heteroepitaxial self-assembled oxide nanostructures.
Giant Enhancement of Ferroelectric Retention in BiFeO3 Mixed-Phase Boundary
(2014-09-24)
Huang, Yen-Chin
;
Liu, Yunya
;
Lin, Yi-Tsu
;
Liu, Heng-Jui
;
He, Qing
A large enhancement of nanodomain retentionis shown in the mixed-phase region of a strained BiFeO3 epitaxial film. The superior ferroelectric retention is attributed to a lower elastic-energy density at the phase boundaries, which act as periodic pinning centers for the domain wall motion. This study delivers a new pathway of incorporating an elastic-energy term to assist ferroelectric retention.
Local Conduction at the BiFeO3-CoFe2O4 Tubular Oxide Interface
(1970-01-01)
Hsieh, Ying-Hui
;
Liou, Jia-Ming
;
Huang, Bo-Chao
;
Liang, Chen-Wei
;
He, Qing
"In strongly correlated oxides, heterointerfaces, manipulating the interaction, frustration, and discontinuity of lattice, charge, orbital, and spin degrees of freedom, generate new possibilities for next generation devices. In this study, existing oxide heterostructures are examined and local conduction at the BiFeO3-CoFe2O4 vertical interface is found. In such heteronanostructures the interface cannot only be the medium for the coupling between phases, but also a new state of the matter. This study demonstrates a novel concept on for oxide interface design and opens an alternative pathway for the exploration of diverse functionalities in complex oxide interfaces."
Magnetic and Magnetodielectric Properties of Epitaxial Iron Vanadate Thin Films
(2017-01)
Zhou, Dongyi
;
Takahashi, Ryota
;
Zhou, Yanyu
;
Kim, Dohyung
;
Suresh, Vandrangi Kumar
The magnetic and magnetodielectric behavior of epitaxial (001) transition metal oxide spinel iron vanadate (Fe1+xV2-xO4, FVO) thin films grown on (001) SrTiO3 substrates by pulsed laser deposition is reported. X-ray absorption spectroscopy studies confirm the trivalent and nominally divalent nature of V and Fe ions, respectively, while an excess of Fe3+ ions is also found. Aberration-corrected cross-sectional scanning transmission electron microscopy analysis suggests that the excess Fe3+ may be accommodated through Fe3O4 stacking faults along the {111} planes. Temperature-dependent X-ray magnetic circular dichroism spectra reveal an anti-parallel alignment of spins between the Fe2+ and V3+ cations. M-H loops acquired at 10 K, well below the noncollinear ferromagnetic phase transition temperature, show magnetic anisotropy and point to the existence of two distinct phases with different coercive fields. Visual evidence for magnetic domains and their switching is given by magnetic force microscopy, which finds a switching field of approximate to 3 T in agreement with the M-H loops. Magnetodielectric measurements for a Pd/FVO/Nb:STO heterostructure reveal a weak hysteresis in the magneto-capacitance loops at 10 K, thus confirming magneto-dielectric coupling. Detailed temperature and frequency-dependent dielectric studies find that Maxwell-Wagner-type relaxation dominates capacitance behavior above approximate to 40 K due to a FVO/Nb:SrTiO3 Schottky interface.
Magnetic and Magnetodielectric Properties of Epitaxial Iron Vanadate Thin Films
(2017-01)
Zhou, Dongyi
;
Takahashi, Ryota
;
Zhou, Yanyu
;
Kim, Dohyung
;
Suresh, Vandrangi Kumar
The magnetic and magnetodielectric behavior of epitaxial (001) transition metal oxide spinel iron vanadate (Fe1+xV2-xO4, FVO) thin films grown on (001) SrTiO3 substrates by pulsed laser deposition is reported. X-ray absorption spectroscopy studies confirm the trivalent and nominally divalent nature of V and Fe ions, respectively, while an excess of Fe3+ ions is also found. Aberration-corrected cross-sectional scanning transmission electron microscopy analysis suggests that the excess Fe3+ may be accommodated through Fe3O4 stacking faults along the {111} planes. Temperature-dependent X-ray magnetic circular dichroism spectra reveal an anti-parallel alignment of spins between the Fe2+ and V3+ cations. M-H loops acquired at 10 K, well below the noncollinear ferromagnetic phase transition temperature, show magnetic anisotropy and point to the existence of two distinct phases with different coercive fields. Visual evidence for magnetic domains and their switching is given by magnetic force microscopy, which finds a switching field of approximate to 3 T in agreement with the M-H loops. Magnetodielectric measurements for a Pd/FVO/Nb:STO heterostructure reveal a weak hysteresis in the magneto-capacitance loops at 10 K, thus confirming magneto-dielectric coupling. Detailed temperature and frequency-dependent dielectric studies find that Maxwell-Wagner-type relaxation dominates capacitance behavior above approximate to 40 K due to a FVO/Nb:SrTiO3 Schottky interface.