Direct observation of electronic structure change by resistance random access memory effect in amorphous alumina

Kubota, Masato; Nigo, Seisuke*; Kato, Seiichi*; Amemiya, Kenta*

AIP Advances (Internet), 9(9), p.095050_1 - 095050_4, 2019/09

https://doi.org/10.1063/1.5086212

We measured the X-ray absorption spectra of amorphous alumina with vacancy-type oxygen defects which exhibits the resistance random access memory effect. For the first time, we detected changes in the electronic structure owing to the memory effect. A major difference in spectrum was observed near the O K-absorption edge.

Spin orientation transition across the single-layer graphene/nickel thin film interface

Matsumoto, Yoshihiro; Entani, Shiro; Koide, Akihiro*; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Fujikawa, Takashi*; Sakai, Seiji

Journal of Materials Chemistry C, 1(35), p.5533 - 5537, 2013/09

https://doi.org/10.1039/C3TC30872C

Electronic and spin states of single- and bi-layer graphene on ferromagnetic metal

Matsumoto, Yoshihiro; Entani, Shiro; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Sakai, Seiji

no journal, , 

no abstracts in English

Spin-polarized states of the CVD-grown graphene on the Ni(111) substrate

Matsumoto, Yoshihiro; Entani, Shiro; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Sakai, Seiji

no journal, , 

Electronic and spin states at single layer graphene / Ni interface; A Depth-resolved XMCD study

Matsumoto, Yoshihiro; Entani, Shiro; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Sakai, Seiji

no journal, , 

no abstracts in English

X-ray absorption and magnetic circular dichroism signals from hexagonal boron nitride/Ni(111) interface

Otomo, Manabu; Matsumoto, Yoshihiro; Yamamura, Noyuri*; Entani, Shiro; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Fujikawa, Takashi*; Sakai, Seiji

no journal, , 

Graphene has been intensively studied in the last few years for its long spin coherent length. The performance of graphene spintronic devices, however, are strongly influenced by poor spin injection efficiency at graphene/ferromagnetic metal (FM) interface. A promising solution for improving spin injection efficiency is to insert a tunnel barrier between graphene and FM. In this study, we propose hexagonal boron nitride (h-BN) as a novel tunnel barrier for graphene spintronics. It was revealed that the N K-edge and B K-edge absorptions exhibit XMCD signals in response to the Ni magnetization. It was also found that the smaller incidence angle between the Ni magnetization and the X-ray propagation direction leads to larger XMCD signals. The nature of the spin polarization was discussed in connection with the energy and angle dependences of the XMCD signals, and contribution from magnetized Nickel atoms was proposed.

Depth-resolved X-ray magnetic circular dichroism spectroscopy on single- and bi-layer graphene / Ni structures

Matsumoto, Yoshihiro; Entani, Shiro; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Sakai, Seiji

no journal, , 

In the present study, the electronic and magnetic states of the graphene/FM interface are investigated for the single-layer graphene (SLG)/Ni(111) and bilayer graphene (BLG)/Ni(111) structures by using the depth-resolved X-ray magnetic circular dichroism (XMCD) spectroscopy. For the SLG/Ni(111) structure, an intense XMCD signal was observed in the C K-edge XMCD spectrum measured by reversing the remanent magnetization of Ni(111). This indicates that spin polarization is induced in the -orbitals of SLG by the contact with Ni(111) even at room temperature. More interestingly, the BLG/Ni(111) structure is found to show the C K-edge XMCD signal whose intensity changes dramatically with the probing depth. On the other hand, the depth-resolved analysis of the Ni L-edge XMCD spectrum demonstrated that the magnetization of Ni decreases by 20-30 % within a few atomic layers from the graphene (SLG, BLG)/Ni(111) interfaces, possibly associated with the formation of C-Ni bonds.

Depth-resolved XMCD study on single- and bi-layer graphene / Ni structure

Matsumoto, Yoshihiro; Entani, Shiro; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Sakai, Seiji

no journal, , 

The interaction of graphene with a metal is of both fundamental and technological interest in view of possible device applications. In the present study, depth-resolved X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) spectroscopy have been applied to the single layer graphene (SLG) grown on the Ni(111) substrate by ultrahigh vacuum chemical vapor deposition method to clear the electronic and spin states in the graphene/ferromagnetic metal interface. As a results, the intense XMCD signal derived from SLG is successfully detected, which indicates that the spin polarization in SLG is induced by Ni magnetization. And it is also found that the observed XMCD intensity is drastically changed depending on the probing depth. As for the Ni layer, the magnetization of the Ni atoms near the interface is decreased by 20-30% than that of Ni atoms far from the interface. This is considered that the magnetic structures of Ni atoms are changed by the formation of C-Ni bond.

Spin orientation transition across the graphene/nickel thin film interface

Matsumoto, Yoshihiro; Entani, Shiro; Koide, Akihiro*; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Fujikawa, Takashi*; Sakai, Seiji

no journal, , 

Spin orientation and electronic states at graphene/nickel interface

Matsumoto, Yoshihiro*; Entani, Shiro; Koide, Akihiro*; Otomo, Manabu*; Avramov, P.*; Naramoto, Hiroshi*; Amemiya, Kenta*; Fujikawa, Takashi*; Sakai, Seiji

no journal, , 

no abstracts in English