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Hirohata, Atsufumi*; Lloyd, D. C.*; Kubota, Takahide*; Seki, Takeshi*; Takanashi, Koki; Sukegawa, Hiroaki*; Wen, Z.*; Mitani, Seiji*; Koizumi, Hiroki*
IEEE Access, 11, p.117443 - 117459, 2023/10
Times Cited Count：2 Percentile：13.47(Computer Science, Information Systems)Kusano, Kanya*; Ichimoto, Kiyoshi*; Ishii, Mamoru*; Miyoshi, Yoshizumi*; Yoden, Shigeo*; Akiyoshi, Hideharu*; Asai, Ayumi*; Ebihara, Yusuke*; Fujiwara, Hitoshi*; Goto, Tadanori*; et al.
Earth, Planets and Space (Internet), 73(1), p.159_1 - 159_29, 2021/12
Times Cited Count：7 Percentile：44.49(Geosciences, Multidisciplinary)The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.
Kim, J.*; Sinha, J.*; Mitani, Seiji*; Hayashi, Masamitsu*; Takahashi, Saburo*; Maekawa, Sadamichi; Yamanouchi, Michihiko*; Ohno, Hideo*
Physical Review B, 89(17), p.174424_1 - 174424_8, 2014/05
Times Cited Count：95 Percentile：93.90(Materials Science, Multidisciplinary)We have studied the underlayer thickness and temperature dependencies of the current-induced effective field in CoFeB/MgO heterostructures with Ta-based underlayers. The underlayer thickness at which the effective field saturates is found to be different between the two orthogonal components of the effective field; i.e., the dampinglike term tends to saturate at a smaller underlayer thickness than the fieldlike term. For large underlayer thickness films in which the effective field saturates, we find that the measurement temperature significantly influences the size of the effective field. A striking difference is found in the temperature dependence of the two components: the dampinglike term decreases whereas the fieldlike term increases with increasing temperature. Using a simple spin diffusion-spin transfer model, we find that all of these results can be accounted for provided the real and imaginary parts of an effective spin mixing conductance are negative. These results imply that either spin transport in this system is different from conventional metallic interfaces or effects other than spin diffusion into the magnetic layer need to be taken into account in order to model the system accurately.
Kasai, Shinya*; Hirayama, Yusuke*; Takahashi, Yukiko*; Mitani, Seiji*; Hono, Kazuhiro*; Adachi, Hiroto; Ieda, Junichi; Maekawa, Sadamichi
Applied Physics Letters, 104(16), p.162410_1 - 162410_4, 2014/04
Times Cited Count：16 Percentile：50.64(Physics, Applied)
-Co films with current-perpendicular-to-plane geometrySakai, Seiji; Mitani, Seiji*; Matsumoto, Yoshihiro; Entani, Shiro; Avramov, P.; Otomo, Manabu; Naramoto, Hiroshi*; Takanashi, Koki
Journal of Magnetism and Magnetic Materials, 324(12), p.1970 - 1974, 2012/06
Times Cited Count：3 Percentile：14.12(Materials Science, Multidisciplinary)Hayashi, Masamitsu*; Ieda, Junichi; Yamane, Yuta; Oe, Junichiro*; Takahashi, Yukiko*; Mitani, Seiji*; Maekawa, Sadamichi
Physical Review Letters, 108(14), p.147202_1 - 147202_5, 2012/04
Times Cited Count：40 Percentile：82.71(Physics, Multidisciplinary)Spinmotive force associated with a moving domain wall is observed directly in permalloy nanowires using real time voltage measurements with proper subtraction of the electromotive force. Whereas the wall velocity exhibits nonlinear dependence on a magnetic field, the generated voltage increases linearly with the field. We show that the sign of the voltage reverses when the wall propagation direction is altered. Numerical simulations explain quantitatively these features of spinmotive force and indicate that the spinmotive force scales with the field even in a field range where the wall motion is no longer associated with periodic structure transformation.
-Co filmsSakai, Seiji; Mitani, Seiji*; Sugai, Isamu; Takanashi, Koki; Matsumoto, Yoshihiro; Entani, Shiro; Naramoto, Hiroshi*; Avramov, P.; Maeda, Yoshihito
Physical Review B, 83(17), p.174422_1 - 174422_6, 2011/05
Times Cited Count：8 Percentile：34.92(Materials Science, Multidisciplinary)-Co granular thin filmsSugai, Isamu*; Sakai, Seiji; Matsumoto, Yoshihiro; Naramoto, Hiroshi*; Mitani, Seiji*; Takanashi, Koki; Maeda, Yoshihito
Journal of Applied Physics, 108(6), p.063920_1 - 063920_7, 2010/09
Times Cited Count：8 Percentile：33.69(Physics, Applied)-Co films with giant tunnel magnetoresistanceMatsumoto, Yoshihiro; Sakai, Seiji; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Mitani, Seiji*; Naramoto, Hiroshi*; Maeda, Yoshihito
Chemical Physics Letters, 470(4-6), p.244 - 248, 2009/03
Times Cited Count：17 Percentile：50.22(Chemistry, Physical)Electronic and spin states of the codeposited C-Co films with large tunnel magnetoresistance (TMR) effect were investigated with the X-ray absorption and magnetic circular dichroism (MCD) spectroscopies. It is revealed that a C-Co compound generated in the C-Co films shows the clear MCD signal attributed to the spin-polarized Co 3d states hybridized with C 
orbitals. The magnetic response of these Co 3d-derived states agrees well with temperature dependence of the observed MR ratios of the granular C-Co films. This suggests the incorporation of the spin-polarized Co 3d-derived states of the C-Co compound into the observed TMR effect.
Sakai, Seiji; Sugai, Isamu; Mitani, Seiji*; Takanashi, Koki; Matsumoto, Yoshihiro; Naramoto, Hiroshi*; Avramov, P.; Okayasu, Satoru; Maeda, Yoshihito
Applied Physics Letters, 91(24), p.242104_1 - 242104_3, 2007/12
Times Cited Count：30 Percentile：71.18(Physics, Applied)-Co film with high magnetoresistanceSakai, Seiji; Yakushiji, Kei*; Mitani, Seiji*; Sugai, Isamu; Takanashi, Koki*; Naramoto, Hiroshi*; Avramov, P.; Lavrentiev, V.*; Narumi, Kazumasa; Maeda, Yoshihito
Materials Transactions, 48(4), p.754 - 758, 2007/04
Times Cited Count：9 Percentile：50.56(Materials Science, Multidisciplinary)Magnetic properties were investigated for the alternately deposited film of C and Co which has found to exhibit tunnel magnetoresistance (MR) of 10-80 %. Magnetic field and temperature dependences of magnetization showed typical superparamagnetic behaviors with the blocking temperature of 40 K. The magnetization curve at 300 K was well fitted by the Langevin function with the size distribution of Co particles, and the mean diameter and size distribution were evaluated to be 3.1 nm and 1 nm, respectively. Based on the magnetic properties, the detailed structure and magnetotransport properties are discussed.
compound hybrid systemSakai, Seiji; Yakushiji, Kei*; Mitani, Seiji*; Takanashi, Koki*; Naramoto, Hiroshi; Avramov, P.; Narumi, Kazumasa; Lavrentiev, V.; Maeda, Yoshihito
Applied Physics Letters, 89(11), p.113118_1 - 113118_3, 2006/09
Times Cited Count：59 Percentile：85.84(Physics, Applied)In this study, the first results are described on the spin-dependent transport in the Co-C hybrid film in which Co nanoparticles are dispersed in a matrix of the Co-C compound. It is found that the hybrid film shows significant tunnel magnetoresistance (MR) of a few 10 %, which is comparable to granular metal-insulator systems, under the small applied bias voltage. Additionally, it is found that the electrical conductivity and MR ratio are strongly influenced by the bias voltage and the MR ratio under the higher bias voltage reaches 80%, which is anomalously high in granular systems. The bias-dependent magnetotransport behaviours are surmised to be related to the electronic structure of the Co-C compound.
Sakai, Seiji; Sugai, Isamu; Mitani, Seiji*; Matsumoto, Yoshihiro; Takanashi, Koki; Naramoto, Hiroshi*; Avramov, P.; Okayasu, Satoru; Maeda, Yoshihito
no journal, ,
-Co hybrid filmsSakai, Seiji; Matsumoto, Yoshihiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Naramoto, Hiroshi*; et al.
no journal, ,
no abstracts in English
Sugai, Isamu; Sakai, Seiji; Mitani, Seiji*; Matsumoto, Yoshihiro; Takanashi, Koki; Naramoto, Hiroshi*; Avramov, P.; Okayasu, Satoru; Maeda, Yoshihito
no journal, ,
no abstracts in English
Sakai, Seiji; Sugai, Isamu; Mitani, Seiji*; Matsumoto, Yoshihiro; Takanashi, Koki; Naramoto, Hiroshi*; Okayasu, Satoru; Maeda, Yoshihito
no journal, ,
no abstracts in English
-Co thin filmsSakai, Seiji; Matsumoto, Yoshihiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Maeda, Yoshihito
no journal, ,
no abstracts in English
-Co compound / Ni bilayer thin filmMatsumoto, Yoshihiro; Entani, Shiro; Shimada, Toshihiro*; Naramoto, Hiroshi*; Mitani, Seiji*; Takanashi, Koki; Yokoyama, Toshihiko*; Sakai, Seiji
no journal, ,
no abstracts in English
Sakai, Seiji; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki*; Naramoto, Hiroshi*; Avramov, P.; Okayasu, Satoru; Narumi, Kazumasa; Maeda, Yoshihito
no journal, ,
no abstracts in English
-Co thin films with current-perpendicular-to-plane devise structuresSakai, Seiji; Matsumoto, Yoshihiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Maeda, Yoshihito
no journal, ,
no abstracts in English
