Nonreciprocity in spin waves is of great interest in both fundamental science and applications because it offers an extra knob to control the flow of waves for the technological fields of logics and switch applications. We show a high nonreciprocity in spin waves from Ta/Py bilayer systems with out-of-plane magnetic fields [1].

The magnetic tunnel junction (MTJ) is a central element for the magnetoresistive random access memory (MRAM). We show that the tunneling magnetoresistance (TMR) of the MTJ is strongly influenced by strain in MTJs, and demonstrate flexible MTJs on various substrates [2], which can be utilized for future flexible MRAMs.

Current induced spin-orbit torques (SOTs) provide a new way to manipulate the magnetization in MTJs. We examine the role of oxygen bonding in Pt/CoFeB/MgO, and find that a full sign reversal of SOTs occurs as the oxygen bonding level increases, which evidences an interfacial SOT mechanism. We show current induced SOTs from multilayer nanowires such as Co/Pd and ferrimagnetic CoGd systems [3]. SOTs in a topological insulator Bi2Se3 as well as an oxide heterostructure LAO/STO show the largest SOTs obtained to date, which generate strong spin currents to switch the magnetization in SOT-MRAM.

We also report on the direct imaging of chiral spin structures including skyrmions in an exchange-coupled Co/Pd multilayer at room temperature with Lorentz transmission electron microscopy. [4] Finally, we discuss the generation of THz for heavy metal/ferromagnet structures using spin orbit torques [5].

Hyunsoo Yang earned his bachelor's degree in electrical engineering from the Seoul National University in 1998 and M.S. and Ph.D. degrees in the electrical engineering department of Stanford University in 2003 and 2006, respectively. From 1988 he worked at a circuit and system design company, earning a patent award, until 2001, when he enrolled in Stanford's graduate school on a scholarship from the Korean Ministry of Information and Communications. He had been working on long-wavelength photonic devices at Stanford university. Since 2004, he had been at IBM-Stanford Spintronic Science and Applications Center. His doctoral research focused on the metal spintronics, especially magnetic tunnel junctions for the magnetic random access memory application. He was awarded the fellowship in the conference on Magnetism and Magnetic Materials for 2005 and the American Physical Society (GMAG) outstanding dissertation award for 2006. He joined the National University of Singapore in the department of Electrical and Computer Engineering in 2007 and is working on various nanomaterials and devices for future electronic applications.

Department of Physics and Astronomy

1. J. H. Kwon et al., Sci. Adv. 2, e1501892 (2016)
2. L. M. Loong et al., Adv. Mat. 28, 4983 (2016)
3. R. Mishra et al., Phys. Rev. Lett. 118, 167201 (2017)
4. S. Pollard et al., Nat. Commun. 8, 14761 (2017)
5. Y. Wu et al., Adv. Mat. 29, 1603031 (2017)

Researchers should cite this work as follows:

• Hyunsoo Yang (2017), "Spin Wave, Skyrmion, and Spin-Orbit Torque Devices," https://nanohub.org/resources/27564.

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