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Journal Articles

Spin colossal magnetoresistance in an antiferromagnetic insulator

Qiu, Z.*; Hou, D.*; Barker, J.*; Yamamoto, Kei; Gomonay, O.*; Saito, Eiji*

Nature Materials, 17(7), p.577 - 580, 2018/05

 Times Cited Count:80 Percentile:96.5(Chemistry, Physical)

Colossal magnetoresistance (CMR) refers to a large change in electrical conductivity induced by a magnetic field in the vicinity of a metal-insulator transition. CMR occurs due to a correlation between the magnetic structure and electron conduction and has inspired extensive studies for decades. Here, in the antiferromagnetic insulator Cr$$_{2}$$O$$_{3}$$, we found a sharp transition between conducting and nonconducting states for spin currents at room temperature. The spin-current transmission changes by two orders of magnitude within a narrow temperature window of 14K around the Neel temperature. The spin conductor-nonconductor transition can be modulated by a magnetic field, giving an isothermal change of spin-current transmission of up to 500%, effectively an on-off switch for spin currents.

Journal Articles

Tunable sign change of spin hall magnetoresistance in Pt/NiO/YIG structures

Hou, D.*; Qiu, Z.*; Barker, J.*; Sato, Koji*; Yamamoto, Kei; V$'e$lez, S.*; Gomez-Perez, J. M.*; Hueso, L. E.*; Casanova, F.*; Saito, Eiji

Physical Review Letters, 118(14), p.147202_1 - 147202_6, 2017/04

 Times Cited Count:90 Percentile:97.62(Physics, Multidisciplinary)

Journal Articles

Fabrication and magnetic control of Y$$_3$$Fe$$_5$$O$$_{12}$$ cantilevers

Seo, Y.-J.*; Harii, Kazuya; Takahashi, Ryo*; Chudo, Hiroyuki; Oyanagi, Koichi*; Qiu, Z.*; Ono, Takahito*; Shiomi, Yuki*; Saito, Eiji

Applied Physics Letters, 110(13), p.132409_1 - 132409_4, 2017/03

 Times Cited Count:12 Percentile:59.19(Physics, Applied)

We have fabricated ferrite cantilevers in which their vibrational properties can be controlled by external magnetic fields. Submicron-scale cantilever structures were made from Y$$_3$$Fe$$_5$$O$$_{12}$$ films by physical etching combined with the use of a focused ion beam milling technique. We found that the cantilevers exhibit two resonance modes which correspond to horizontal and vertical vibrations. Under external magnetic fields, the resonance frequency of the horizontal mode increases, while that of the vertical mode decreases, quantitatively consistent with our numerical simulation for magnetic forces. The changes in resonance frequencies with magnetic fields reach a few percent, showing that an efficient magnetic control of resonance frequencies was achieved.

Journal Articles

Spin-current probe for phase transition in an insulator

Qiu, Z.*; Li, J.*; Hou, D.*; Arenholz, E.*; N'Diaye, A. T.*; Tan, A.*; Uchida, Kenichi*; Sato, Koji*; Okamoto, Satoshi*; Tserkovnyak, Y.*; et al.

Nature Communications (Internet), 7, p.12670_1 - 12670_6, 2016/08

 Times Cited Count:119 Percentile:97.35(Multidisciplinary Sciences)

Journal Articles

Origin of the spin Seebeck effect in compensated ferrimagnets

Gepr$"a$gs, S.*; Kehlberger, A.*; Coletta, F.*; Qiu, Z.*; Guo, E.-J.*; Schulz, T.*; Mix, C.*; Meyer, S.*; Kamra, A.*; Althammer, M.*; et al.

Nature Communications (Internet), 7, p.10452_1 - 10452_6, 2016/02

 Times Cited Count:120 Percentile:97.23(Multidisciplinary Sciences)

Journal Articles

Extending resonant inelastic X-ray scattering to the extreme ultraviolet

Wray, L. A.*; Huang, S.-W.*; Jarrige, I.*; Ikeuchi, Kazuhiko*; Ishii, Kenji; Li, J.*; Qiu, Z. Q.*; Hussain, Z.*; Chuang, Y.-D.*

Frontiers in Physics (Internet), 3, p.32_1 - 32_11, 2015/05

 Times Cited Count:4

Journal Articles

Spin current generation from sputtered Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ films

Lustikova, J.*; Shiomi, Yuki*; Qiu, Z.*; Kikkawa, Takashi*; Iguchi, Ryo*; Uchida, Kenichi*; Saito, Eiji

Journal of Applied Physics, 116(15), p.153902_1 - 053902_6, 2014/10

 Times Cited Count:45 Percentile:87.46(Physics, Applied)

Journal Articles

Performance of vanadium redox flow battery with a novel amphoteric ion exchange membrane synthesized by two-step grafting method

Qiu, J.*; Zhai, M.*; Chen, J.; Wang, Y.*; Peng, J.*; Xu, L.*; Li, J.*; Wei, G.*

Journal of Membrane Science, 342(1-2), p.215 - 220, 2009/10

 Times Cited Count:73 Percentile:91.32(Engineering, Chemical)

A novel ETFE-based amphoteric ion exchange membrane (AIEM) was prepared through a two-step radiation induced grafting technique. ETFE film was first grafted with styrene (St) (denoted as ETFE-$$g$$-PS), followed with a sulfonation treatment to obtain a cation exchange membrane (ETFE-$$g$$-PSSA). The ETFE-$$g$$-PSSA membrane was subsequently grafted with dimethylaminoethyl methacrylate (DMAEMA) and then protonated, resulting in an AIEM with both anionic and cationic groups. The obtained AIEM exhibited high ion exchange capacity (IEC) and conductivity, as well as significantly reduced permeability of vanadium ions. Vanadium redox flow battery (VRFB) assembled with the AIEM maintained an open circuit voltage (OCV) higher than 1.3V after placed for 300h, and exhibited higher columbic efficiency and energy efficiency than that with Nafion117 membrane.

Journal Articles

Amphoteric ion exchange membrane synthesized by radiation-induced graft copolymerization of styrene and dimethylaminoethyl methacrylate into PVDF film for vanadium redox flow battery applications

Qiu, J.*; Zhang, J.*; Chen, J.; Peng, J.*; Xu, L.*; Zhai, M.*; Li, J.*; Wei, G.*

Journal of Membrane Science, 334(1-2), p.9 - 15, 2009/05

 Times Cited Count:83 Percentile:93.37(Engineering, Chemical)

Poly(vinylidene difluoride) (PVDF) film was grafted with styrene (St) and dimethylaminoethyl methacrylate (DMAEMA) using irradiation techniques. Through subsequent sulfonation and protonation processes, a new kind of amphoteric ion exchange membrane (AIEM) was synthesized. The grafting yield ($$GY$$) increased with absorbed dose and leveled off at about 60 kGy. The properties of the AIEM strongly depended on the composition and $$GY$$ of the film, i.e. higher content of DMAEMA brought lower permeability of vanadium ions and conductivity. Finally, an AIEM was assembled and tested in the vanadium redox flow battery (VRFB) system. It was found that the VRFB assembled with the AIEM maintained an open circuit voltage (OCV) higher than 1.2V after placed for 68h, which was much longer than that with the Nafion117 membrane. Therefore, this work provides a novel method to develop potential substitute of Nafion membranes to be applied in VRFB system.

Journal Articles

In situ EXAFS study on GeS$$_{2}$$ glass under high-pressure

Miyauchi, Koichi*; Qiu, J.*; Shojiya, Masanori*; Kawamoto, Yoji*; Kitamura, Naoyuki*; Fukumi, Kohei*; Katayama, Yoshinori; Nishihata, Yasuo

Solid State Communications, 124(5-6), p.189 - 193, 2002/10

 Times Cited Count:7 Percentile:39.4(Physics, Condensed Matter)

A GeS$$_{2}$$ glass was compressed up to 8 GPa at room temperature, heated up to 270 $$^{circ}$$C under 8 GPa and then decompressed to ambient pressure at room temperature, using a large volume high-pressure apparatus. The local structural-changes around Ge were examined by means of EXAFS method. The Ge-S bond length became monotonously short with increasing applied-pressure up to 8 GPa at room temperature. When the specimen was heated to 270 $$^{circ}$$C under 8 GPa, however, the vond length became slightly long. The elongated bond lengthe was almost kept even after the temperature was descended to room tempertature. In decompression process, the bond length became gradually long with releasing applied-pressure down to 2 GPa, following a change in compression process. Below 2 GPa, however, the Ge-S bond length was largely elongated, being lnger than the initial one. No significant change of coordination number was found in the compression and decompression processes up to 8 GPa. This change canbe explained by a combined effect of elastic and inelastic structural-changes.

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