Presented by Dr. Matthias Benjamin Jungfleisch
Materials Science Division, Argonne National Laboratory

Abstract
Creation and manipulation of magnetization states by spin-orbital torques are important for novel spintronics applications. Magnetic insulators were mostly ignored for this particular purpose, despite their low Gilbert damping [1], which makes them ideal materials for magnonic applications and investigation of nonlinear spin-wave phenomena.

Using Brillouin light scattering (BLS) microscopy on micron-scaled scaled yttrium iron garnet (Y₃Fe₅O₁₂,YIG) stripes, we observe long spin-wave propagation distances [1]. We also explored the possibility of driving magnetization dynamics with spin Hall effects (SHE) in bilayers of YIG/Pt microstructures. For this purpose we adopted a spin-transfer torque ferromagnetic resonance (ST-FMR) approach. Here a rf charge current is passed through the Pt layer, which generates a spin-transfer torque at the interface from an oscillating spin current via the SHE. This gives rise to a resonant excitation of the magnetization dynamics. In all metallic systems the magnetization dynamics is detected via the homodyne anisotropic magnetoresistance of the ferromagnetic layer.  However, since there is no charge flowing through ferromagnetic insulators there is no anisotropic magnetoresistance.  Instead, we show that for the case of YIG/Pt the spin Hall magnetoresistance can be used. Our measured voltage spectra can be well fitted to an analytical model evidencing that the ST-FMR concept can be extended to insulating systems [2,3]. Furthermore, we employ spatially-resolved BLS spectroscopy to map the ST-FMR driven spin dynamics. We observe the formation of a strong, self-localized spin-wave intensity in the center of the sample [3]. We furthermore developed a new pathway for lithographically defining patterned YIG structures with submicron dimensions [4], which enables to further investigate the influence of geometric confinement.

The work at Argonne was supported by the U.S. Department of Energy, Office of Science, Materials Science and Engineering Division.

[1] M. B. Jungfleisch et al., J. Appl. Phys. 117, 17D128 (2015).

[2] J. Sklenar et al., Phys. Rev. B 92, 174406 (2015).

[3] M. B. Jungfleisch et al., Phys. Rev. Lett. 116, 057601 (2016).

[4] S. Li, et al., Nanoscale 8, 388 (2016).

Bio
Benjamin Jungfleisch received his Ph.D. in physics from University of Kaiserslautern, Germany. Currently, he is a postdoctoral appointee in the Materials Science Division, Argonne National Laboratory.

He is working in the field of spin dynamics and material properties of magnetic thin films and multilayers. The main focus of his work is on magnon spintronics, a subfield of spintronics concerned with nanoscaled devices and structures that use spin currents carried by magnons.