第 15 回 CSIS セミナー
第 87 回ナノ・スピン工学研究会
スピントロニクス国際共同大学院セミナー
半導体スピントロニクス研究室講演会の開催について日時：

平成 28 年 2 月 18 日（木）10:30～12:00

場所：

電気通信研究所

講師：

Professor Geoffrey Beach

ナノ・スピン総合研究棟 4 階

401 号室MIT Department of Materials Science and Engineering, Cambridge, MA,USA（東北大学電気通信研究所客員准教授）

講演題目： Spin-Orbitronics: Interfacial Design of Spintronic Materials
and Devices
概要：

There is great interest in electrically manipulating the magnetization in nanoscale materials forhigh-performance memory and logic device applications.
In this talk I will describe
recently-discovered mechanisms, based on symmetry breaking and spin-orbit coupling at interfaces,
whereby the magnetization can be controlled using very low currents1-6 or by a gate voltage alone.5-8 I
will focus on ultrathin transition metal ferromagnets sandwiched between an oxide and a nonmagnetic
heavy metal, in which magnetic, electronic and ionic effects at the interface can be exploited in new
and unexpected ways.
I first focus on the heavy-metal/ferromagnetic interface, where spin-orbit coupling influences
not only spin transport, but the nature of magnetism itself in the ferromagnet. In nonmagnetic heavy
metals, spin-orbit coupling leads to a left-right scattering asymmetry such that spin “up” and spin
“down” electrons pile up on either side of a material when a charge current flows through it. I willshow how this spin Hall effect can be used to drive magnetization switching and domain wall motion inan adjacent ferromagnetic film,1-4 and discuss its enhancement through interface engineering5. In thesesame materials, broken inversion symmetry can lift the chiral degeneracy and generate new topologicalspin textures such as spin-spirals and skyrmions through the interfacial Dzyaloshinskii-Moriya
interaction (DMI). I will show that chiral magnetism can persist at room temperature in common
transition metal ferromagnets3,4, and discuss the role of DMI in domain wall dynamics3,4 and spin-orbit
torque switching5. I then show that DMI in engineered heterostructures can be used to stabilize
room-temperature magnetic skyrmions6, which have recently been proposed as scalable,
thermally-stable bits for advanced spintronics devices. We have demonstrated the ability to generate
stable skyrmion lattices and drive trains of individual skyrmions by short current pulses along amagnetic racetrack at speeds exceeding 100 m/s, opening the door to room-temperature skyrmion
spintronics in robust thin-film heterostructures6.
Finally, I will turn to the ferromagnet/oxide interface7-11 and describe our discovery of a newclass of “magneto-ionic” materials,9,10 in which a gate voltage can be used to electrochemically switch
the interfacial oxidation state to realize unprecedented control over magnetic properties. Here we use
Pt/Co/Gd2O3-d ultrathin film stacks, where Gd2O3-d serves as an efficient oxygen ion conductor. Ishow that the magnetization in the thin Co layer can be switched between perpendicular and in-planeorientations, or quenched entirely, by driving O2- towards or away from the Co/GdOx interface with asmall gate voltage10. I then show that magneto-ionic gates can be used to locally tune magnetic
properties to create a magnetic analog of field-effect transistors,9 and to electrically control spin-orbit
torques11.
1.

S. Emori, D. Bono, and G. S. D. Beach, Appl. Phys. Lett. 101, 042405 (2012).

2.

S. Emori, U. Bauer, S.-M. Ahn, E. Martinez, and G. S. D. Beach, Nature Materials 12, 611 (2013).

3.

S. Emori, E. Martinez, Kyung-Jin Lee, Hyun-Woo Lee, U. Bauer, S.-M. Ahn, P. Agrawal, D. C.
Bono, and G. S. D. Beach, Physical Review B 90, 184427 (2014).

4.

N. Perez, E. Martinez, L. Torres, S.-H. Woo, S. Emori, and G. S. D. Beach, Appl. Phys. Lett. 104,092403 (2014)

5.

S. Woo, M. Mann, A. J. Tan, L. Caretta, and G. S. D. Beach, Appl. Phys. Lett. 105, 212404 (2014).

6.

S. Woo, K. Litzius, B. Krüger, M.-Y. Im, L. Caretta, K. Richter, M. Mann, A. Krone, R. Reeve, M.
Weigand, P. Agrawal, P. Fischer, M. Kläui, and G. S. D. Beach, Nature Materials in press (2016);
arXiv:1502.07376

7.

U. Bauer, M. Przybylski, J. Kirschner, and G. S. D. Beach, Nano Lett. 12, 1437 (2012).

8.

U. Bauer, S. Emori, and G. S. D. Beach, Appl. Phys. Lett. 100, 192408; ibid 101, 172403 (2012).

9.

U. Bauer, S. Emori, and G. S. D. Beach, Nature Nanotechnology 8, 411 (2013).

10. U. Bauer, L. Yao, S. Emori, H. L. Tuller, S. van Dijken, and G. S. D. Beach, Nature Materials 14,174 (2015)11. S. Emori, U. Bauer, S. –H. Woo, and G. S. D. Beach, Appl. Phys. Lett.105, 222401 (2014).

☆

☆

問い合わせ先： WPI-AIMR 松倉（片平 5554）
通研・大野研・深見（片平5555）