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Thickness dependence of transport behaviors in SrRuO3 /SrTiO3 superlattices
(2020-01-03)
Wu, Ping-Chun
;
Song, Haili
;
Yuan, Ye
;
Feng, Bin
;
Ikuhara, Yuichi
Ultrathin oxide films have attracted considerable attention due to the potential for the integration of next-generation devices. However, the transport behaviors of the ultrathin oxide films are yet to be explored due to the high resistance caused by the strong influence of the interface and substrates. In this paper, an attempt is made to engineer the transport behaviors in ultrathin oxides. To exclude the high-resistance issue, conductive SrRuO3 with thickness down to two unit cells is embedded in insulating SrTiO3 in the form of superlattices. With precise control of the thickness in each layer, the transport behaviors, as well as the anomalous Hall effects, in SrRuO3 can be systematically manipulated. The analysis indicates that the diversity of the anomalous Hall effects is attributed to the change of Berry curvatures. The results give a pathway to the control of physical properties in ultrathin oxide systems by thickness engineering.
Pulsed laser deposition of complex oxide heteroepitaxy
(2019-08-01)
Huang, Yen-Lin
;
Liu, Heng-Jui
;
Ma, Chun-Hao
;
Yu, Pu
;
Chu, Ying-Hao
The modern studies of complex oxides have been mainly driven by the development of advanced growth and characterization techniques, which provide researchers unprecedented access to new insights and functionalities of these materials. Epitaxial growth of thin films and related architectures offers a pathway to the discovery and stabilization of a wide spectrum of new possibilities in conjunction with the availability of high quality materials that produced with larger lateral sizes and being grown constrainedly. Compared with conventional growth techniques, such as sputtering, spin coating, sol-gel processes, metal-organic chemical vapor deposition, molecular beam epitaxy and so on, no other single advance in the creation of oxide materials has had as pronounced an impact as pulsed laser deposition. In pursuit of the fruitful functionalities and exciting physical phenomena among complex oxides, pulsed laser deposition technique has played an important role to fulfill the flurry of complex oxides in recent decades. In this article, we focus on the details of the growth of epitaxial oxide thin films and the related polymorphs, as well as recent advances in control of the oxide heteroepitaxy via pulsed laser deposition.
Manipulate the Electronic and Magnetic States in NiCo2O4 Films through Electric-Field-Induced Protonation at Elevated Temperature
(2019-04-19)
Wang, Meng
;
Sui, Xuelei
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Wang, Yujia
;
Juan, Yung-Hsiang
;
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.
Nanoscale Control of Domain Architectures in BiFeO3 Thin Films
(2009-04-01)
Chu, Ying-Hao
;
He, Qing
;
Yang, Chan-Ho
;
Yu, Pu
;
Martin, Lane W.
We demonstrate an approach to create a one-dimensional nanoscale array of domain walls in epitaxial La-substituted BiFeO3 films. We have used a DySCO3 (110)(o) single-crystal substrate to provide an anisotropic strain to exclude two of the possible structural variants. Furthermore, through careful control of electrostatic boundary conditions, such as the thickness of the SrRuO3 bottom electrode to induce the self-poling effects, we can choose to obtain either 1090 or 710 one-dimensional periodic domain walls. Detailed measurements of the domain structures is shown using piezoresponse force microscopy and X-ray diffraction, which confirms that these periodic structures are the same as those suggested in previous literature.
Tailoring Magnetoelectric Coupling in BiFeO3/La0.7Sr0.3MnO3 Heterostructure through the Interface Engineering
(2019-03-15)
Yi, Di
;
Yu, Pu
;
Chen, Yi-Chun
;
Lee, Hsin-Hua
;
He, Qing
Electric field control of magnetism ultimately opens up the possibility of reducing energy consumption of memory and logic devices. Electric control of magnetization and exchange bias are demonstrated in all-oxide heterostructures of BiFeO3 (BFO) and La0.7Sr0.3MnO3 (LSMO). However, the role of the polar heterointerface on magnetoelectric (ME) coupling is not fully explored. Here, the ME coupling in BFO/LSMO heterostructures with two types of interfaces, achieved by exploiting the interface engineering at the atomic scale, is investigated. It is shown that both magnetization and exchange bias are reversibly controlled by switching the ferroelectric polarization of BFO. Intriguingly, distinctly different modulation behaviors that depend on the interfacial atomic sequence are observed. These results provide new insights into the underlying physics of ME coupling in the model system. This study highlights that designing interface at the atomic scale is of general importance for functional spintronic devices.
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.
Atomically Resolved Electronic States and Correlated Magnetic Order at Termination Engineered Complex Oxide Heterointerfaces
(2018-02-01)
Huang, Bo-Chao
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Yu, Pu
;
Chu, Y. H.
;
Chang, Chia-Seng
;
Ramesh, Ramamoorthy
We map electronic states, band gaps, and interface-bound charges at termination-engineered BiFeO3/La0.7Sr0.3MnO3 interfaces using atomically resolved cross-sectional scanning tunneling microscopy. We identify a delicate interplay of different correlated physical effects and relate these to the ferroelectric and magnetic interface properties tuned by engineering the atomic layer stacking sequence at the interfaces. This study highlights the importance of a direct atomically resolved access to electronic interface states for understanding the intriguing interface properties in complex oxides.
Anomalous Electronic Anisotropy Triggered by Ferroelastic Coupling in Multiferroic Heterostructures
(2016-02-03)
Ju, Changcheng
;
Yang, Jan-Chi
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Luo, Cheng
;
Shafer, Padraic
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Liu, Heng-Jui
Strain-Mediated Inverse Photoresistivity in SrRuO3/La0.7Sr0.3MnO3 Superlattices
(2016-02-02)
Liu, Heng-Jui
;
Wei, Tzu-Chiao
;
Zhu, Yuan-Min
;
Liu, Rui-Rui
;
Tzeng, Wen-Yen
In the pursuit of novel functionalities by utilizing the lattice degree of freedom in complex oxide heterostructure, the control mechanism through direct strain manipulation across the interfaces is still under development, especially with various stimuli, such as electric field, magnetic field, light, etc. In this study, the superlattices consisting of colossal-magnetoresistive manganites La0.7Sr0.3MnO3 (LSMO) and photostrictive SrRuO3 (SRO) have been designed to investigate the light-dependent controllability of lattice order in the corresponding functionalities and rich interface physics. Two substrates, SrTiO3 (STO) and LaAlO3 (LAO), have been employed to provide the different strain environments to the superlattice system, in which the LSMO sublayers exhibit different orbital occupations. Subsequently, by introducing light, we can modulate the strain state and orbital preference of LSMO sublayers through light-induced expansion of SRO sublayers, leading to surprisingly opposite changes in photoresistivity. The observed photoresistivity decreases in the superlattice grown on STO substrate while increases in the superlattice grown on LAO substrate under light illumination. This work has presented a model system that demonstrates the manipulation of orbital-lattice coupling and the resultant functionalities in artificial oxide superlattices via light stimulus.
Heteroepitaxy of Fe3O4/Muscovite: A New Perspective for Flexible Spintronics
(2016-12-14)
Wu, Ping-Chun
;
Chen, Ping-Fan
;
Thi Hien Do
;
Hsieh, Ying-Hui
;
Ma, Chun-Hao
Spintronics has captured a lot of attention since it was proposed. It has been triggering numerous research groups to make their efforts on pursuing spin-related electronic devices. Recently, flexible and wearable devices are in a high demand due to their outstanding potential in practical applications. In order to introduce spintronics into the realm of flexible devices, we demonstrate that it is feasible to grow epitaxial Fe3O4 film, a promising candidate for realizing spintronic devices based on tunneling magnetoresistance, on flexible muscovite. In this study, the heteroepitaxy of Fe3O4/muscovite is characterized by X-ray diffraction, high-resolution transmission electron microscopy, and Raman spectroscopy. The chemical composition and magnetic feature are investigated by a combination of X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism. The electrical and magnetic properties are examined to show the preservation of the primitive properties of Fe3O4. Furthermore, various bending tests are performed to show the tunability of functionalities and to confirm that the heterostructures retain the physical properties under repeated cycles. These results illustrate that the Fe3O4/muscovite heterostructure can be a potential candidate for the applications in flexible spintronics.

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