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Journal Articles

Effect of cotunneling and spin polarization on the large tunneling magnetoresistance effect in granular C $_{60}$ -Co films

Sakai, 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

https://doi.org/10.1103/PhysRevB.83.174422

Times Cited Count：8 Percentile：34.63(Materials Science, Multidisciplinary)

Journal Articles

Surface-assisted spin Hall effect in Au films with Pt impurities

Gu, B.; Sugai, Isamu*; Ziman, T.*; Guo, G. Y.*; Nagaosa, Naoto; Seki, Takeshi*; Takanashi, Koki; Maekawa, Sadamichi

Physical Review Letters, 105(21), p.216401_1 - 216401_4, 2010/11

https://doi.org/10.1103/PhysRevLett.105.216401

Times Cited Count：71 Percentile：89.84(Physics, Multidisciplinary)

Journal Articles

Composition dependence of magnetic and magnetotransport properties in C $_{60}$ -Co granular thin films

Sugai, 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

https://doi.org/10.1063/1.3471800

Times Cited Count：8 Percentile：33.38(Physics, Applied)

Journal Articles

The Electronic structures of fullerene/transition-metal hybrid material

Matsumoto, Yoshihiro; Sakai, Seiji; Naramoto, Hiroshi*; Hirao, Norie*; Baba, Yuji; Shimada, Toshihiro*; Sugai, Isamu; Takanashi, Koki; Maeda, Yoshihito

Materials Research Society Symposium Proceedings, Vol.1081 (Internet), 6 Pages, 2008/03

Recently, we have found the appearance of substantial MR ratio (80%) in a C $_{60}$ /Co hybrid material. Such the MR ratio cannot be explained enough only by tunnel conduction through Co grains. Therefore, to obtain information about electronic structures of C $_{60}$ /Co hybrid material is necessary. Absorption spectra of C $_{60}$ Co are different from that of pristine C $_{60}$ . In particular, peak intensity corresponding to (LUMO) C 1s excitation of C $_{60}$ Co is clearly attenuated. In addition, C 1s photoelectron peak of C $_{60}$ Co slightly shifted to lower binding energy compared to that of pristine C $_{60}$ . These results indicate that 3d electron of Co transfers to orbital of C $_{60}$ and new electronic states are formed in the C $_{60}$ -Co compound. In fact, XPS spectra of valence excitation region also demonstrate the formation of hybrid orbital near the Fermi level due to the coupling of C $_{60}$ and Co.

Journal Articles

Giant tunnel magnetoresistance in codeposited fullerene-cobalt films in the low bias-voltage regime

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

https://doi.org/10.1063/1.2822397

Times Cited Count：30 Percentile：70.91(Physics, Applied)

Journal Articles

Magnetic and magnetotransport properties in nanogranular Co/C $_{60}$ -Co film with high magnetoresistance

Sakai, 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

https://doi.org/10.2320/matertrans.48.754

Times Cited Count：10 Percentile：54.76(Materials Science, Multidisciplinary)

Magnetic properties were investigated for the alternately deposited film of C $_{60}$ 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.

Oral presentation

Spin-polarized current flow in the C $_{60}$ -Co hybrid films with giant TMR effect

Sakai, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Maeda, Yoshihito

no journal, ,

no abstracts in English

Oral presentation

Tunnel magnetoresistance in granular Co-C $_{60}$ hybrid films

Sakai, Seiji; Sugai, Isamu; Yakushiji, Kei*; Mitani, Seiji*; Takanashi, Koki*; Naramoto, Hiroshi; Avramov, P.; Narumi, Kazumasa; Maeda, Yoshihito

no journal, ,

no abstracts in English

Oral presentation

Tunneling magnetotransport in hybrid system of cobalt and C $_{60}$

Sakai, Seiji; Sugai, Isamu; Yakushiji, Kei*; Mitani, Seiji*; Takanashi, Koki*; Naramoto, Hiroshi; Avramov, P.; Narumi, Kazumasa; Maeda, Yoshihito

no journal, ,

We have revealed that the Co/Co-C $_{60}$ films prepared by alt-deposition show the tunnel MR of a few 10% under low bias voltage and the further enhancement to above 80% by the voltage increase at lower temperature than 10 K. In the present study, the magnetotransport properties in the co-deposited Co/Co-C $_{60}$ films are reported. The co-deposited film shows the remarkable tunnel MR effect (10-50%) whose ratio is significantly influenced by the applied voltage. Such a significant MR enhancement by the bias-voltage is found to take place commonly in the Co/Co-C $_{60}$ films irrespective of the deposition method, and that is in contrast to the small extent of changes in the conventional metal/insulator systems. In the presentation, the comparative results for the co-deposited and alt-deposited Co/Co-C $_{60}$ films are also reported in comparison with the analyzed structures by Raman spectroscopy et al..

Oral presentation

Giant TMR effect and spin states of C $_{60}$ -Co thin films

Sakai, 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

Oral presentation

Electronic and spin states and giant tunnel magnetoresistance effect in C $_{60}$ -Co hybrid films

Sakai, 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

Oral presentation

Systematic study of magneto-transport properties of C $_{60}$ -Co films with giant tunnel magnetoresistance

Sakai, Seiji; Matsumoto, Yoshihiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Naramoto, Hiroshi*; Okayasu, Satoru; Maeda, Yoshihito

no journal, ,

no abstracts in English

Oral presentation

Effect of highly spin-polarized interfaces on giant tunnel magnetoresistance in granular structured C $_{60}$ -Co films

Sakai, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Naramoto, Hiroshi*; Maeda, Yoshihito

no journal, ,

no abstracts in English

Oral presentation

Analysis of giant tunnel magnetoresistance effect in granular C60-Co films

Sakai, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Naramoto, Hiroshi*; Maeda, Yoshihito

no journal, ,

no abstracts in English

Oral presentation

Giant TMR effect and interface spin-polarization of C60-Co films

Sakai, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Naramoto, Hiroshi*; Maeda, Yoshihito

no journal, ,

no abstracts in English

Oral presentation

Higly spin-polarized current in C $_{60}$ -Co films

Sakai, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Sugai, Isamu*; Takanashi, Koki; Mitani, Seiji*; Naramoto, Hiroshi*; Maeda, Yoshihito

no journal, ,

no abstracts in English

Oral presentation

Highly spin-polarized tunneling current in C $_{60}$ -Co granular films

Sakai, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Naramoto, Hiroshi*; Maeda, Yoshihito

no journal, ,

no abstracts in English

Oral presentation

Composition dependence of tunnel magnetoresistance in C $_{60}$ -Co thin films

Sakai, Seiji; Sugai, Isamu; Matsumoto, Yoshihiro; Mitani, Seiji*; Takanashi, Koki; Naramoto, Hiroshi*; Avramov, P.; Okayasu, Satoru; Maeda, Yoshihito

no journal, ,

no abstracts in English

Oral presentation

Giant tunnel magnetoresistance and interface spin-polarization in granular C60-Co films

Sakai, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Sugai, Isamu*; Takanashi, Koki; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Naramoto, Hiroshi*; et al.

no journal, ,

We investigated the bias-voltage (V) and temperature (T) dependences of the spin-dependent transport properties of the granular C60-Co films in the current perpendicular to plane (CPP) geometry. At low T, each sample shows much higher MR than the upper limit of TMR (MR=50%) derived from the Julliere's model. From the I-V characteristics, we evaluated the degree of the higher order tunneling process, as a possible cause of the MR enhancement above MR=50%, to be 3-7 (T=2K), which changes depending on the sample composition and device structure. By considering this enhancement effect, we can estimate the spin-polarization at the C60-Co compound/Co interface. The estimated values are remarkably high, i.e., P=75% at zero temperature, compared to Co crystal(P=30%), and almost independent of the samples. The detailed results on the transport properties and X-ray magnetic circular dichroism spectroscopy were presented in the conference.

Oral presentation

Highly spin-polarized tunnel magnetoresistance in granular C $_{60}$ -Co films

Sakai, Seiji; Matsumoto, Yoshihiro; Entani, Shiro; Sugai, Isamu*; Takanashi, Koki; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Naramoto, Hiroshi*; et al.

no journal, ,

In the present study, we examine the bias-voltage (V) and temperature (T) dependences of the spin-dependent transport properties of the granular C $_{60}$ -Co films (C $_{60}$ Co $_{6-10}$ ) in the current perpendicular to plane (CPP) geometry for the origin of the large TMR effect. At low T, the CPP samples show much higher MR than the upper limit of TMR (MR = 50%) derived from the Julliere's model. From the I-V characteristics, we evaluated the degree of the higher order tunneling process, as a possible cause of the MR enhancement above MR = 50%, to be 3-7 at low temperatures, which changes depending on the sample composition and device structure. After considering this MR enhancement effect, we can evaluate the spin-polarization of the tunneling electrons generated at the C $_{60}$ -Co compound/Co interface. The evaluated values are remarkably high, i.e., P 75% at zero temperature, compared to Co crystal (P = 30%).