第 13 回 CSIS セミナー
第 85 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 4 日（木）16:00～17:30

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： Magnetic domain walls in thin-film nanostructures:

Statics, dynamics, and emerging applications
概要：
Domains of opposing magnetization direction in a ferromagnet are separated by narrow transitions

called domain walls. Ferromagnetic nanowires provide a well-defined conduit for domain walls, which
may be manipulated by magnetic fields or electric currents and used in a variety of information storage
and processing schemes [1]. This seminar will describe the static and dynamic properties of domain walls,
their interactions with spin currents, and how these properties can be engineered in nanoscale materials
and device geometries.
In thicker magnetic films the magnetostatic energy dominates: domains lie in the plane and thestructure and dynamics [2] of nanowire-guided domain walls are dictated principally by the geometry. In
this case the domain walls are typically quite wide, and while they can be driven by current through bulk
spin-transfer torques [3,4], the high critical currents and low velocities present a challenge to eventual
applications. In ultrathin films, broken symmetry and spin-orbit coupling (SOC) at interfaces can give riseto an interfacial contribution to the magnetic anisotropy that can dominate if the film is sufficiently thin,pulling the magnetization out of the plane and leading to domain walls with a width of just a few nm.
While the influence of interfacial SOC on magnetic anisotropy has been recognized for decades, theimpacts on spin transport and spin textures in ultrathin-film heterostructures have only recently to come tolight. In nonmagnetic heavy metals such as Pt and Ta with strong SOC, conduction elecrons exhibit aleft-right scattering asymmetry such that spin “up” and spin “down” electrons pile up on either side of amaterial when a charge current flows through it. This spin Hall effect can be used to create pure spincurrents at the interface that can efficiently drive magnetization switching and domain wall motion in anadjacent ferromagnetic film [5,6]. At the same time, broken inversion symmetry and spin-orbit couplingcan lead to an antisymmetric exchange interaction known as the Dzyaloshinskii-Moriya (DM) interaction,
which competes with the usual Heisenberg exchange to generate nonuniform spin textures with a preferredchirality [6]. This seminar will describe the origin and consequences of this interaction on domain walls
and their dynamics [6,7], as well as other topologically nontrivial textures such as magnetic skyrmions thathave very recently been observed at room temperature [8].
1. S.S.P. Parkin, M. Hayashi, and L. Thomas, Science 320, 190 (2008).
2. G. S. D. Beach, C. Nistor, C. Knutson, M. Tsoi, and J. L. Erskine, Nature Mater. 4, 741 (2005).
3. G.S.D. Beach, C. Knutson, C. Nistor, M. Tsoi, and J. L. Erskine, Phys. Rev. Lett. 97, 057203 (2006).
4. G. S. D. Beach, M. Tsoi, and J. Erskine, J. Magn. Magn. Mater. 320, 1272 (2008).
5. L. Liu, C.-F. Pai, Y. Li, H.W. Tseng, D.C. Ralph, and R.A. Buhrman, Science 336, 555 (2012).
6. S. Emori, U. Bauer, S.-M. Ahn, E. Martinez, and G. S. D. Beach, Nature Materials 12, 611 (2013).
7. E. Martinez, S. Emori, N. Perez, L. Torres and G. S. D. Beach, J. Appl. Phys. 115, 213909 (2014).
8. S. Woo, et al., arXiv:1502.07376 (2015); to be published in Nature Materials.

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