Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-14

Magnetoresistance effects in spin-valves comprising Fe3Si/N-doped carbon/Fe
trilayered films
Satoshi Takeichi1, Kazuki Kudo1, Kazutoshi Nakashima1, Ken-ichiro Sakai2, and Tsuyoshi
Yoshitake1
1 Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka
816-8580, Japan.
2
Department of Control and Information Systems Engineering, National Institute of Technology,
Kurume College, Kurume, Fukuoka 830-8555, Japan.

Abstract
Trilayered spin-valves composed of ferromagnetic Fe3Si and Fe layers and nitrogen-doped carbon
interlayers were prepared on Si(111) substrates by a mask method, and the injection and transportof polarized carriers were experimentally studied from their magnetic and electrical evaluations.
Here, the nitrogen-doped carbon layers were deposited by coaxial arc plasma deposition (CAPD) inthe same manner as the deposition of nitrogen-doped ultrananocrystalline diamond(UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films comprising alarge number of nanodiamond grains embedded in an a-C:H matrix. The shape of a magnetization
curve had clear steps, This evidently indicates the formation of antiparallel alignment of themagnetization owing to a difference in the coercive force between the top polycrystalline Fe andbottom epitaxial Fe3Si layers. Curiously, the magnetoresistance (MR) curve of the trilayers exhibits
negative signal corresponding to the formation of antiparallel magnetization alignments, so-called“inverse MR effects”, which is completely opposite from behavior of the conventional spin-valves
that exhibit positive signals.

representative application candidates [6]. For
the application to spin-transistors, spin
injection from ferromagnetic metals into
semiconductors and spin transport insemiconductors are key. It is expected thatmaterials composed of light elements possesslong spin-transport lengths due to weak spinorbit interactions. In particular, carbon-basedmaterials such as graphene and carbon
nanotube (CNT) have received muchattention as promising materials of spintransport [7,8].
In the recent decade, our laboratory
has investigated the semiconducting
characteristics
ofultrananocrystalline
diamond (UNCD)/hydrogenated amorphous
carbon (a-C:H) composite (UNCD/a-C:H)
films comprising a large number of nanosized diamond grains and an a-C:H matrix,
prepared by coaxial arc plasma deposition(CAPD) [9-13]. We have experimentallydemonstrated that they can be deposited on
foreign solid substrates at low substrate

1. Introduction
Electronics and magnetics that utilize
electric charge and spin of electrons,
respectively, have progressed almost
independently until the discovery of giant
magnetoresistance (GMR) effects [1,2].
Spintronics is the fusion field of electronics
and magnetics, and have attracted
considerable attention from physical andpractical viewpoints, because both electriccharge and spin of electrons are utilized
simultaneously.
GMRandtunnel
magnetoresistance (TMR) [3-5] effects havebeen the main principles of spintronics
devices such as hard disk heads, which usechanges in the electrical resistanceaccompanied by switching between parallel
and antiparallel magnetization alignments.
Whereas GMR and TMR films
employ nonmagnetic metal and insulator asinterlayers, respectively, semiconductor
spintronics has also extensively been
investigated.
Spin-transistors
are40

Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-14
temperatures by CAPD and p and n-types
conduction can be produced by boron andnitrogen doping.
According to previous reports, n-type
Si and Ge have longer spin diffusion lengths
than those of p-type ones [14-17] and thepolarization of MR effects seems not to bedependent on the conduction type. And
organic semiconductors exhibits inverse MReffects. Here, note that variable range
hopping is predominant in UNCD/a-C:H,
similarly to organic semiconductors.
In this work, trilayered spin-valves
comprising ferromagnetic Fe3Si and Fe
electrodes and nitrogen-doped UNCD/a-C:H
interlayer were prepared by physical vapor
deposition combined with a mask method,
and they were studied structurally,magnetically, and electrically.

(a)

(b)

Figure 1. Schematic diagram of (a) deposition
procedure of Fe/nitrogen-doped UNCD/Fe3Si
trilayers and (b) electrical circuit for MR curvemeasurement.

2. Experimental
Fe (100 nm)/nitrogen-doped UNCD (10nm)/Fe3Si (100 nm) trilayered spin-valves
were prepared on p-type Si(111) substrates bya mask method. The deposition procedure of
the trilayers is shown in Fig. 1(a). Firstly,
natural oxide on the p-type Si(111) substrate
having specific resistances in the range of
3000-8000 Ω·cm was removed with 0.5%hydrofluoric acid and rinsed in deionizedwater as the pretreatment of substrates.
Secondly, the bottom Fe3Si layer wasdeposited on the Si(111) substrate at an Ar
pressure of 1.33 × 10-1 Pa and substratetemperature of 300 °C, by facing target
direct-current sputtering (FTDCS) using the
1st mask. Subsequently, after the exposure toair for the mask replacement, nitrogen-doped
UNCD/a-C:H interlayer was deposited bycoaxial arc plasma deposition (CAPD) withthe 2nd mask at a substrate temperature of
300 °C under a 53.3 Pa nitrogen andhydrogen mixed gas atmosphere with aninflow ratio between nitrogen and hydrogengases (IN/H) of 1.5. Finally, after theexposure to air for the mask replacement
again, the top Fe layer was deposited with the3rd mask at an argon pressure of 1.33 × 10-1
Pa and room temperature by FTDCS. The
crystallinity of the trilayers was evaluated by

X-ray diffraction (XRD). The magnetization
curves of the trilayers were measured at room
temperature using a vibrating sample
magnetometer (VSM). The electrical circuitfor measuring MR effects is schematicallyshown in Fig. 1(b).
3. Result and Discussion
3.1. Crystallinity
The 2θ-θ XRD patterns of the trilayers
and the Si(111) substrate as a background areshown in Fig. 2(a). Diffraction peaks ofFe3Si-222 and Fe-200 are observed. Figure2(b) shows a pole-figure concerning theFe3Si-422 plane with a rotation axis of Fe3Si[222]. It was confirmed that 111-oriented
crystallites are also in-plane ordered. Totallyconsidering these results and our previous
research [18], the bottom Fe3Si layer is
epitaxially grown on the Si(111) substrate.
Since the Fe layer is deposited on the nonoriented UNCD/a-C:H, it should be
polycrystalline.
3.2 Magnetical and Electrical Properties
Magnetization and MR curves of the41Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-14
trilayers, measured at room temperature, areshown in Fig. 3. The magnetization curve has
clear two steps that indicate the antiparallelalignment formation of magnetizations
owing to the difference in the coercive forces
between the top Fe and bottom Fe3Si layers.
The MR curve was measured at a bias
current of 10 mA. Curiously, corresponding
to the switching of layer magnetizationalignments, the MR curve exhibits a negative
signal. This is because the device-resistancefor the antiparallel magnetization alignment
is lower than that for the parallel alignment ofthe FM electrodes.
The origin of this “inverse MR” isunknown
atpresent.
Inorganic
semiconductors, it is considered that inverse
MR might be induced by an inversion of thespin polarization of the conduction electrons
at the oxide- or hybrid-layer formed between
ferromagnetic electrode and interlayer as
previously
reportedinspin-valves
comprising organic materials such as 8hydroxy-quinoline
aluminium(Alq3),
poly(3-hexylthiophene) (P3HT), and C60[19-21]. For a probable origin, the similar
mechanism is supposed.

(a)
Si 222Fe 200

Fe3Si 222

Intensity (arb. unit)

Si 111(b)trilayers

Si–sub.

204060802 (deg)

Figure 2. (a) 2θ-θ XRD patterns of trilayers, and(b) pole figure concerning Fe3Si-422 planes.

M/Ms

10–1

Resistance ()4. Conclusion
Fe/nitrogen-doped
UNCD/Fe3Si
trilayered spin-valves were prepared by amask method, and the spin-valve behaviors
were magnetically and electrically evaluated.
Due to a difference in the coercive force
between the top polycrystalline Fe andbottom epitaxial Fe3Si layers, the antiparallelalignments of magnetizations were formed.
The polarization of the MR curve is opposite
to that of general metallic spin-valves, whichevidently indicates inverse MR effects.occurs
in this study. As previously reported in spinvalves comprising organic materials, theinverse MR might be induced by oxide- or
hybrid-layer at the interface between FM
electrode and interlayer.

44.78

44.76

–40

–20

02040

Magnetization field (Oe)Figure 3. Magnetization (upper) and MR (lower)
curve of the trilayers, measured at room
temperature.

Yoshida Academic Education Promotion
Association.

Acknowledgment
This work was partially financiallysupported by JSPS KAKENHI Grant
Number JP16K14391 and JP15K21594, andReference42

Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-14[1] G. Binasch, P. Grunberg, F. Saurenbach, and W.

[18] K. Takeda, T. Yoshitake, D. Nakagauchi, T.

Zinn, Phys. Rev. B 39, 4828 (1989).

Ogawa, D. Hara, M. Itakura, N. Kuwano, Y.

[2] M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen

Tomokiyo, T. Kajiwara, and K. Nagayama, Jpn.

Van Dau, F. Petroff, P. Etienne, G. Creuzet, A.

J. Appl. Phys. 46, 7846 (2007).

Friederich, and J. Chazelas, Phys. Rev. Lett. 61,[19] Z. H. Xiong, Di Wu, Z. Valy Vardeny, and Jing

247

Shi, Nature 427, 821 (2004).

(1988).

[20] S. Ding, Y. Tian, Y. Li, W. Mi, H. Dong, X.

[3] M. Julliere, Phys. Lett. 54A, 225 (1975).

Zhang, W. hu, and D. Zhu, ACS Appl. Mater.

[4] S. Maekawa, and U. Gafvert, IEEE Trans. Magn.

Interfaces 9, 15644 (2017).

18, 707 (1982).

[21] K. Yoshida, I. Hamada, S. Sakata, A. Umeno, M.

[5] T. Miyazaki and N. Tezuka, J. Magn. Magn.

Tsukada, and K. Hirakawa, Nano Lett. 13, 481

Mater. 139, L231 (1995).

(2013).

[6] S. Sugahara, and M. Tanaka, Appl. Phys. Lett. 84,2307 (2004)[7] M. Shiraishi, Jpn. J. Appl. Phys. 51, 08KA01(2012).
[8] K. Tsukagoshi, BW. Alphenaar, and H. Ago,
Nature 401, 572 (1999).
[9] T. Yoshitake, A. Nagano, M. Itakura, N. Kuwano,T. Hara, and K. Nagayama, Jpn. J. Appl. Phys.
46, L936 (2007).
[10] T. Yoshitake, Y. Nakagawa, A. Nagano, R.
Ohtani, H. Setoyama, E. Kobayashi, K.
Sumitani, Y. Agawa, and K. Nagayama, Jpn. J.
Appl. Phys. 49, 015503 (2010).
[11] S. Ohmagari, T. Yoshitake, A. Nagano, R.
Ohtani, H. Setoyama, E. Kobayashi, T. Hara,and K. Nagayama, Jpn. J. Appl. Phys. 49,031302 (2010).
[12] S. Ohmagari and T. Yoshitake, Jpn. J. Appl.
Phys. 51, 090123 (2012).
[13] Y. Katamune, S. Ohmagari, S. Al-Riyami, S.
Takagi, M. Shaban, and T. Yoshitake, Jpn. J.
Appl. Phys. 52, 065801 (2013).
[14] S. P. Dash, S. Sharma, R. S. Patel, M. P. de Jong,and R. Jansen, Nature 462, 491 (2009) .
[15] T. Suzuki, T. Sasaki, T. Oikawa, M. Shiraishi, Y.
Suzuki, and K. Noguchi, Appl. Phys. Express 4,023003 (2011).
[16] S. Iba, H. Saito, A. Spiesser, S. Watanabe, R.
Jansen, S. Yuasa, and K. Ando, Appl. Phys.
Express 5, 053004 (2003).
[17] K. Kasahara, Y. Baba, K. Yamane, Y. Ando, Y.
Hoshi, K. Sawano, M. Miyao, and K. Hamaya,J. Appl. Phys. 111, 07C503 (2012).

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