Browsing by Author "Kaun, Chao-Cheng"

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GdFe0.8Ni0.2O3: A Multiferroic Material for Low-Power Spintronic Devices with High Storage Capacity
(2019-08-28)
Chang, Shu-Jui
;
Chung, Ming-Han
;
Kao, Ming-Yi
;
Lee, Shang-Fan
;
Yu, Yi-Hsing
Multiferroic materials are strong candidates for reducing the energy consumption of voltage-controlled spintronic devices because of the coexistence of ferroelectric (FE) and magnetic orders in a single phase. In this article, we present a new multiferroic perovskite, GdNixFe1-xO3 (GFNO), produced via sputtering on a SrTiO3 substrate. The proposed GFNO is FE and canted antiferromagnetic (AFM) within a monoclinic framework at room temperature. The FE polarization of the GFNO is up to 37 mu C/cm(2). When capped with a Co layer, the resulting heterostructure exhibits voltage-controlled magnetism (VCM). The heterostructured device exhibits two distinct features. First, its VCM depends on the magnitude as well as the polarity of the applied bias, thereby doubling the number of available magnetic readout states under a fixed voltage. Furthermore, the magnetic order of the device can be controlled very effectively within +/- 1 V. These two characteristics satisfy the requirements for low-power and high-storage technology. Theoretical analysis and experimental results indicate the importance of Ni dopant in regulating the polarity-dependent multiferroicity of this gadolinium ferrite system.
Spin filtering of a termination-controlled LSMO/Alq(3) heterojunction for an organic spin valve
(2017-09-21)
Lam, Tu-Ngoc
;
Huang, Yen-Lin
;
Weng, Ke-Chuan
;
Lai, Yu-Ling
;
Lin, Ming-Wei
La1-xSrxMnO3 (LSMO) is weLL known as an efficient spin-injection electrode in ferromagnetic organic hybrid-based organic spin valves (OSV). Herein, we examine the influence of three terminating Layers of LSMO fiLms (mixed-, MnO2-, and LaSrO- (LSO-) terminated) on the spin filter at the bottom interface of tri (8-hydroxyquinoLine) aluminum (ALq(3)) deposited on these substrates. Angle-dependent X-ray photoelectron spectra (XPS) demonstrated the presence of SrO segregation at the outermost Layer for three types of LSMO fiLms but in different amounts that might contribute to their magnetic properties. A weak surface coupling between LSMO and Alq(3) was obtained through a small increase of Mn L-edge X-ray magnetic circular dichroism (XMCD) but it does not vary the bulk magnetic properties of LSMO fiLms upon Alq(3) adsorption (LSMO/Alq(3)). The surface dipoles due to the interaction between LSMO fiLms and Alq(3) were found to be 0.5, 0.5, and 0.7 eV for the mixed-ter/Alq(3), MnO2-ter/Alq(3), and LSO-ter/Alq(3) interfaces, respectively. Our results indicate that the segregated SrO Layer Ways an important role in the surface electronic and magnetic properties at LSMO/Alq(3) interfaces, which contributes to a fundamental understanding of the spin injection and transport in LSMO-Alq(3) hybrid-based OSV devices.
Thermoelectric Charge and Spin Current Generation in Magnetic Single-Molecule Junctions: First-Principles Calculations
(2018-06-14)
Kaun, Chao-Cheng
;
Chen, Yu-Chang
;
電子物理學系
;
Department of Electrophysics
We apply first-principles approaches to investigate the spin (charge) Seebeck effects [S-s(c)] and spin (charge) thermoelectric figure of merits [ZT(s(c)) of manganese-phthalocyanine spin-polarized scanning tunneling microscopy (MnPc SP-STM) junctions. The magnetic tunneling junctions are N-type junctions because their S-c values are negative. Their S-s and S-c values are sufficiently large for the efficient generation of measurable spin and charge currents. ZTs(c) values strongly depend on the competition between electron and phonon thermal conductances: ZT(s(c)) proportional to S-s(c)(2) for K-ph << K-ei, and ZT(s(c)) proportional to S-s(c)2(x) k(el) for K-el << K-ph. S-s changes signs when the spin-valve junction rotates its magnetic structure from the antiparallel (AP) to the parallel (P) configuration. This behavior indicates that spin-current direction can be reversed by alternating magnetic configurations between AP and P states. Spin-current dissipation in-the junctions is minimized because the sizes of the junctions are considerably smaller than the lengths of spin flip scattering and spin dephasing. The low spin-current dissipation of the junctions suggests that they have potential applications in spintronics and renewable energy. The present finding provides a new approach to spin-current generation through the use of SP-STM based on temperature difference and to controlling spin-current direction through magnetic configurations. The integration of numerous single-molecule magnetic junctions as building blocks into a high density device is a promising strategy for generating a considerable net spin current for applications in molecular spin caloritronics.