Browsing by Author "Arenholz, Elke"

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Anomalous Electronic Anisotropy Triggered by Ferroelastic Coupling in Multiferroic Heterostructures
(2016-02-03)
Ju, Changcheng
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Yang, Jan-Chi
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Luo, Cheng
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Shafer, Padraic
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Liu, Heng-Jui
Complex strain evolution of polar and magnetic order in multiferroic BiFeO3 thin films
(2018-09-21)
Chen, Zuhuang
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Chen, Zhanghui
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Kuo, Chang-Yang
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Tang, Yunlong
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Dedon, Liv R.
Electric-field control of magnetism requires deterministic control of the magnetic order and understanding of the magnetoelectric coupling in multiferroics like BiFeO3 and EuTiO3. Despite this critical need, there are few studies on the strain evolution of magnetic order in BiFeO3 films. Here, in (110)-oriented BiFeO3 films, we reveal that while the polarization structure remains relatively unaffected, strain can continuously tune the orientation of the antiferromagnetic-spin axis across a wide angular space, resulting in an unexpected deviation of the classical perpendicular relationship between the antiferromagnetic axis and the polarization. Calculations suggest that this evolution arises from a competition between the Dzyaloshinskii-Moriya interaction and single-ion anisotropy wherein the former dominates at small strains and the two are comparable at large strains. Finally, strong coupling between the BiFeO3 and the ferromagnet Co0.9Fe0.1 exists such that the magnetic anisotropy of the ferromagnet can be effectively controlled by engineering the orientation of the antiferromagnetic-spin axis.
Design of magnetoelectric coupling in a self-assembled epitaxial nanocomposite via chemical interaction
(2014)
Liang, Wen I.
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Liu, Yuangming
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Liao, Sheng Chieh
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Wang, Wei Cheng
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Liu, Heng Jui
A chemically induced magnetoelectric coupling effect in ferroelectric/antiferromagnetic self-assembled vertical nanocomposites is designed. A concrete connection between chemical diffusion and the induced magnetic moment is revealed. Importantly, this study shows the strong magnetoelectric coupling effect, which is key to extend the design of functionality in vertical nanocomposites.
Electrical Control of Multiferroic Orderings in Mixed-Phase BiFeO3 Films
(2012-06-12)
Chen, Yi-Chun
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He, Qing
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Chu, Feng-Nan
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Huang, Yen-Chin
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Chen, Jhih-Wei
Electrically enhanced magnetization in highly strained BiFeO3 films
(2016-05)
Yang, Jan-Chi
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Kuo, Chang-Yang
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Liu, Heng-Jui
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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 Structural and Magnetic Coupling in a Mesocrystal-Assisted Nanocomposite
(2016-01-20)
Zhu, Yuanmin
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Zhan, Qian
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Yang, Jan-Chi
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Bitla, Yugandhar
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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
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Chen, Long-Yi
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He, Qing
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Liang, Chen-Wei
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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.
Magnetic Mesocrystal-Assisted Magnetoresistance in Manganite
(2014-11-01)
Yang, Jan-Chi
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He, Qing
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Zhu, Yuan-Min
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Lin, Jheng-Cyuan
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Liu, Heng-Jui
Mesocrystal, a new class of crystals as compared to conventional and well-known single crystals and polycrystalline systems, has captured significant attention in the past decade. Recent studies have been focused on the advance of synthesis mechanisms as well as the potential on device applications. In order to create further opportunities upon functional mesocrystals, we fabricated a self-assembled nanocomposite composed of magnetic CoFe2O4 mesocrystal in Sr-doped manganites. This combination exhibits intriguing structural and magnetic tunabilities. Furthermore, the antiferromagnetic coupling of the mesocrystal and matrix has induced an additional magnetic perturbation to spin-polarized electrons, resulting in a significantly enhanced magnetoresistance in the nanocomposite. Our work demonstrates a new thought toward the enhancement of intrinsic functionalities assisted by mesocrystals and advanced design of novel mesocrystal-embedded nanocomposites.
Manipulate the Electronic and Magnetic States in NiCo2O4 Films through Electric-Field-Induced Protonation at Elevated Temperature
(2019-04-19)
Wang, Meng
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Sui, Xuelei
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Wang, Yujia
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Juan, Yung-Hsiang
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Lyu, Yingjie
Ionic-liquid-gating- (ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO2.5, VO2, WO3, etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo2O4, an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo2O4 from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution.
Tuning the Competition between Ferromagnetism and Antiferromagnetism in a Half-Doped Manganite through Magnetoelectric Coupling
(2013-09-18)
Yi, Di
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Liu, Jian
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Okamoto, Satoshi
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Jagannatha, Suresha
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Chen, Yi-Chun
We investigate the possibility of controlling the magnetic phase transition of the heterointerface between a half-doped manganite La0.5Ca0.5MnO3 and a multiferroic BiFeO3 (BFO) through magnetoelectric coupling. Using macroscopic magnetometry and element-selective x-ray magnetic circular dichroism at the Mn and Fe L edges, we discover that the ferroelectric polarization of BFO controls simultaneously the magnetization of BFO and La0.5Ca0.5MnO3 (LCMO). X-ray absorption spectra at the oxygen K edge and linear dichroism at the Mn L edge suggest that the interfacial coupling is mainly derived from the superexchange between Mn and Fe t(2g) spins. The combination of x-ray absorption spectroscopy and mean-field theory calculations reveals that the d-electron modulation of Mn cations changes the magnetic coupling in LCMO, which controls the enhanced canted moments of interfacial BFO via the interfacial coupling. Our results demonstrate that the competition between ferromagnetic and antiferromagnetic instability can be modulated by an electric field at the heterointerface, providing another pathway for the electrical field control of magnetism.
Tuning the magnetic properties of self-assembled BiFeO3-CoFe2O4 heteroepitaxy by magneto-structural coupling
(2016)
Amrillah, Tahta
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Vandrangi, Suresh K.
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Bitla, Yugandhar
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Do, Thi Hien
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Liao, Sheng-Chieh
Magnetic and multiferroic nanocomposites with two distinct phases have been a topic of intense research for their profound potential applications in the field of spintronics. In addition to growing high-quality phase separated heteroepitaxial nanocomposites, the strain engineering that is conducive to enhance the tunability of material properties, in general, and the magnetic properties, in particular, is of utmost importance in exploring new possibilities. Here, we investigated the magneto-structural coupling between anti-ferromagnetic BiFeO3 (BFO) and ferrimagnetic CoFe2O4 (CFO) in self-assembled vertically aligned nanocomposites grown on LaAlO3 (LAO) and SrTiO3 (STO) substrates. We found that BFO exhibits tetragonal (T) and rhombohedral (R) structures as the stable phases and CFO has high magnetocrystalline anisotropy even in the form of nanocomposites. The temperature and magnetic field dependent magnetizations of T_ BFO-CFO/LAO and R_ BFO-CFO/STO nanocomposites primarily demonstrate the magnetoelastic coupling between these variants.
Van der Waals epitaxy of functional MoO2 film on mica for flexible electronics
(2016-06-20)
Ma, Chun-Hao
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Lin, Jheng-Cyuan
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Liu, Heng-Jui
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Thi Hien Do
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Zhu, Yuan-Min
Flexible electronics have a great potential to impact consumer electronics and with that our daily life. Currently, no direct growth of epitaxial functional oxides on commercially available flexible substrates is possible. In this study, in order to address this challenge, muscovite, a common layered oxide, is used as a flexible substrate that is chemically similar to typical functional oxides. We fabricated epitaxial MoO2 films on muscovite via pulsed laser deposition technique. A combination of X-ray diffraction and transmission electron microscopy confirms van der Waals epitaxy of the heterostructures. The electrical transport properties of MoO2 films are similar to those of the bulk. Flexible or free-standing MoO2 thin film can be obtained and serve as a template to integrate additional functional oxide layers. Our study demonstrates a remarkable concept to create flexible electronics based on functional oxides. Published by AIP Publishing.