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Journal Articles

Ferromagnetic interlayer coupling in C$$_{60}$$-Co compound/Ni bilayer structure

Matsumoto, Yoshihiro; Sakai, Seiji; Entani, Shiro; Takagi, Yasumasa*; Nakagawa, Takeshi*; Naramoto, Hiroshi*; Avramov, P.; Yokoyama, Toshihiko*

Chemical Physics Letters, 511(1-3), p.68 - 72, 2011/07

 Times Cited Count:5 Percentile:16.5(Chemistry, Physical)

X-ray magnetic circular dichroism (XMCD) spectroscopy was employed to investigate the electronic and magnetic structures of the bilayers of a C$$_{60}$$-Co compound and Ni. A few -several nm thick C$$_{60}$$-Co compound layers on the Ni(111) surface are found to show intense XMCD signals attributed to the localized Co d-spins only with the remanent magnetization of Ni layer. It is suggested that the region of the C$$_{60}$$-Co compound within 3 nm from the interface is ferromagnetically coupled with Ni due to the indirect exchange interaction mediated by C$$_{60}$$, probably relevant to the interlayer charge transfer.

Journal Articles

X-ray absorption spectroscopy and magnetic circular dichroism in codeposited C$$_{60}$$-Co films with giant tunnel magnetoresistance

Matsumoto, 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:51.45(Chemistry, Physical)

Electronic and spin states of the codeposited C$$_{60}$$-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$$_{60}$$-Co compound generated in the C$$_{60}$$-Co films shows the clear MCD signal attributed to the spin-polarized Co 3d states hybridized with C$$_{60}$$ $$pi$$ orbitals. The magnetic response of these Co 3d-derived states agrees well with temperature dependence of the observed MR ratios of the granular C$$_{60}$$-Co films. This suggests the incorporation of the spin-polarized Co 3d-derived states of the C$$_{60}$$-Co compound into the observed TMR effect.

Oral presentation

Analysis of magnetic properties in C60-Co nanogranular thin film by XMCD spectroscopy

Matsumoto, Yoshihiro; Sakai, Seiji; Naramoto, Hiroshi*; Takagi, Yasumasa*; Nakagawa, Takeshi*; Shimada, Toshihiro*; Yokoyama, Toshihiko*; Maeda, Yoshihito

no journal, , 

no abstracts in English

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

Soft X-ray circular dichroism study of electronic and magnetic states in C$$_{60}$$-Co mixture film

Matsumoto, Yoshihiro; Sakai, Seiji; Naramoto, Hiroshi*; Nakagawa, Takeshi*; Takagi, Yasumasa*; Yokoyama, Toshihiko*; Takanashi, Koki; Mitani, Seiji*; Shimada, Toshihiro*; Maeda, Yoshihito

no journal, , 

no abstracts in English

Oral presentation

Electronic and magnetic states of codeposited C$$_{60}$$-Co films with giant tunnel magnetoresistance effect

Matsumoto, Yoshihiro; Sakai, Seiji; Naramoto, Hiroshi*; Nakagawa, Takeshi*; Takagi, Yasumasa*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Mitani, Seiji*; Takanashi, Koki; Maeda, Yoshihito

no journal, , 

no abstracts in English

Oral presentation

X-ray magnetic circular dichroism of codeposited C60-Co films with giant tunnel magnetoresistance

Matsumoto, Yoshihiro; Sakai, Seiji; Naramoto, Hiroshi*; Nakagawa, Takeshi*; Takagi, Yasumasa*; Yokoyama, Toshihiko*; Hirao, Norie; Baba, Yuji; Shimada, Toshihiro*; Maeda, Yoshihito

no journal, , 

Recently, we have found that the codeposited C60-Co films where Co nanoparticles are dispersed into the matrix of the C60-Co compound show large tunnel magnetoresistanene (TMR) effects at low temperatures. The observed MR ratios cannot be explained by a spin-polarization of crystalline Co, so it is expected that the C60-Co compound mediates an enhancing effects to the spin-dependent transport in the films. In the present work, we have investigated the spin states of the C60-Co films by X-ray magnetic circular dichroism spectroscopy. As the results, MCD spectra of the C60-Co compound show the sensitivity to the sample temperature, which is consistent to the temperature dependence of MR ratios. This indicates clearly that spin-polarized states of the C60-Co compound influences the degree of spin-dependent transport in the films.

Oral presentation

Electronic and spin states of C$$_{60}$$-Co thin films studied by XPS and X-ray magnetic circular dichroism

Matsumoto, Yoshihiro; Sakai, Seiji; Naramoto, Hiroshi*; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Hirao, Norie; Baba, Yuji; Maeda, Yoshihito

no journal, , 

Oral presentation

Electronic and spin states of C$$_{60}$$-Co thin films studied by XPS and X-ray magnetic circular dichroism

Matsumoto, Yoshihiro; Sakai, Seiji; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Mitani, Seiji*; Takanashi, Koki; Shimada, Toshihiro*; Naramoto, Hiroshi*; Maeda, Yoshihito

no journal, , 

no abstracts in English

Oral presentation

Giant TMR effect in Granular-structured C$$_{60}$$-Co hybrid films

Sakai, Seiji; Matsumoto, Yoshihiro; Sugai, Isamu*; Mitani, Seiji*; Takanashi, Koki; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Naramoto, Hiroshi*; Maeda, Yoshihito

no journal, , 

In the present study, the V and T dependences of the TMR effect are investigated intensively for the co-deposited C$$_{60}$$-Co films with different compositions. The mechanism of the giant TMR effect is discussed taking our recent results for the microstructures of the granular films (i.e., a hybrid structure of the covalent C$$_{60}$$-Co compound and Co nanoparticles dispersed therein) and the electronic and spin states of the C$$_{60}$$-Co compound studied by XPS and X-ray magnetic circular dichroism (XMCD) spectroscopy into account.

Oral presentation

Giant TMR effect and spin states in fullerene-cobalt hybirid films

Sakai, Seiji; Matsumoto, Yoshihiro; Mitani, Seiji*; Takanashi, Koki; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Naramoto, Hiroshi*; Maeda, Yoshihito

no journal, , 

Anomalously large tunnel magnetoresistance (TMR) effects were found for the granular structured C60-Co films consisting of a C60-Co compound matrix and Co nanoparticles dispersed therein. The observed MR ratios of 90% at the maximum are significantly higher than the MR ratios of the inorganic granular films. Our recent X-ray magnetic circular dichroism study revealed that the C60-Co compound in the C60-Co films shows the paramagnetic behaviors due to the spin-polarized states (Co d-spin) derived from the Co 3d orbitals. We found that the T-dependence of the zero-bias MR ratio is represented by considering the similar T-dependence of the spin-polarization(P) of tunneling electrons to the observed T-dependence of the magnetization of the Co d-spin in the C60-Co compound, and by assuming P=100% at low temperature. This result suggests the incorporation of the spin-polarized Co 3d-derived states of the C60-Co compound into the spin-transport process in the granular C60-Co films.

Oral presentation

Spin states of the codeposited C$$_{60}$$-Co thin films with giant tunnel magnetoresistance

Matsumoto, Yoshihiro; Sakai, Seiji; Naramoto, Hiroshi*; Nakagawa, Takeshi*; Takagi, Yasumasa*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Mitani, Seiji*; Takanashi, Koki; Maeda, Yoshihito

no journal, , 

no abstracts in English

Oral presentation

Electronic and spin states analysis of C$$_{60}$$-Co compounds affecting giant tunneling magnetoresistance effect

Matsumoto, Yoshihiro; Sakai, Seiji; Entani, Shiro; Nakagawa, Takeshi*; Takagi, Yasumasa*; Yokoyama, Toshihiko*; Nagamatsu, Shinichi*; Shimada, Toshihiro*; Naramoto, Hiroshi*; Mitani, Seiji*; et al.

no journal, , 

no abstracts in English

Oral presentation

X-ray magnetic circular dichroism spectroscopy of codeposited C$$_{60}$$-Co films

Matsumoto, Yoshihiro; Sakai, Seiji; Entani, Shiro; Nakagawa, Takeshi*; Takagi, Yasumasa*; Yokoyama, Toshihiko*; Nagamatsu, Shinichi*; Shimada, Toshihiro*; Naramoto, Hiroshi*; Mitani, Seiji*; et al.

no journal, , 

no abstracts in English

Oral presentation

Soft X-ray magnetic circular dichroism spectroscopy of co deposited C$$_{60}$$-Co thin films

Matsumoto, Yoshihiro; Sakai, Seiji; Entani, Shiro; Nakagawa, Takeshi*; Takagi, Yasumasa*; Nagamatsu, Shinichi*; Yokoyama, Toshihiko*; Shimada, Toshihiro*; Naramoto, Hiroshi*; Mitani, Seiji*; et al.

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%).

Oral presentation

Magnetic properties of C$$_{60}$$-Co compound in granular C$$_{60}$$-Co films with giant TMR effect

Matsumoto, Yoshihiro; Sakai, Seiji; Entani, Shiro; Takagi, Yasumasa*; Nakagawa, Takeshi*; Nagamatsu, Shinichi*; Shimada, Toshihiro*; Naramoto, Hiroshi*; Yokoyama, Toshihiko*; Maeda, Yoshihito

no journal, , 

Recently, we have found that the granular C$$_{60}$$-Co films have revealed the presence of the localized spin-polarized states in the C$$_{60}$$-Co compound, and it was suggested that such localized states are closely correlated with the large tunnel magnetoresistance (TMR) effect. Detailed analysis of the C$$_{60}$$-Co compound is essential for the understanding of the electronic origin of the TMR effect. In the present study, we investigated electronic and spin states of the C$$_{60}$$-Co compound with different Co content, x (C$$_{60}$$Co$$_{x}$$, x $$<$$ 5) using X-ray absorption (XAS) and magnetic circular dichroism (MCD) spectroscopies.

Oral presentation

Magnetic property of highly spin polarized fullerene-cobalt compound/magnetic metal interface

Sakai, Seiji; Matsumoto, Yoshihiro; Otomo, Manabu; Entani, Shiro; Avramov, P.; Naramoto, Hiroshi*; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*

no journal, , 

no abstracts in English

Oral presentation

Electronic and magnetic structure of fullerene-cobalt compound/magnetic metal interface

Sakai, Seiji; Matsumoto, Yoshihiro; Otomo, Manabu; Entani, Shiro; Avramov, P.; Naramoto, Hiroshi*; Takagi, Yasumasa*; Nakagawa, Takeshi*; Yokoyama, Toshihiko*

no journal, , 

no abstracts in English

21 (Records 1-20 displayed on this page)