Emission of Coherent Propagating Magnons by Insulator-Based Spin-Orbit-Torque Oscillators

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Letter

Emission of Coherent Propagating Magnons by Insulator-Based Spin-Orbit-Torque Oscillators

M. Evelt, L. Soumah, A.B. Rinkevich, S.O. Demokritov, A. Anane, V. Cros, Jamal Ben Youssef, G. de Loubens, O. Klein, P. Bortolotti, and V.E. Demidov

Phys. Rev. Applied 10, 041002 – Published 23 October 2018

Abstract

We experimentally demonstrate generation of coherent propagating magnons in ultrathin magnetic insulator films by spin-orbit torque induced by a direct electric current. We show that this challenging task can be accomplished by use of magnetic insulator films with large perpendicular magnetic anisotropy. We demonstrate simple and versatile spin-orbit-torque devices that can be used as highly efficient nanoscale sources of coherent propagating magnons for insulator-based spintronic applications.

Received 23 July 2018
Revised 2 October 2018

DOI:https://doi.org/10.1103/PhysRevApplied.10.041002

Physics Subject Headings (PhySH)

Magnetization dynamics Magnons Spin current Spin torque Spin-orbit coupling Spintronics

Magnetic insulators Ultrathin films

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

M. Evelt¹, L. Soumah², A.B. Rinkevich³, S.O. Demokritov^1,3, A. Anane², V. Cros², Jamal Ben Youssef⁴, G. de Loubens⁵, O. Klein⁶, P. Bortolotti², and V.E. Demidov^1,*

¹Institute for Applied Physics and Center for Nonlinear Science, University of Münster, 48149 Münster, Germany
²Unité Mixte de Physique CNRS/Thales, CNRS, Thales, University Paris-Sud, Université Paris-Saclay, 91767 Palaiseau, France
³Institute of Metal Physics, Ural Division of RAS, Ekaterinburg 620108, Russia
⁴LABSTICC, UMR 6285 CNRS, Université de Bretagne Occidentale, 29238 Brest, France
⁵SPEC, CEA-Saclay, CNRS, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
⁶SPINTEC, CEA-Grenoble, CNRS and Université Grenoble Alpes, 38054 Grenoble, France

^*demidov@uni-muenster.de

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Vol. 10, Iss. 4 — October 2018

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Images

Figure 1
Experimental layout. The device consists of an extended 20-nm-thick $Bi YIG$ film with PMA and a 6-nm-thick $Pt$ line with length of 4 µm and width of 1 µm. The direct current I in $Pt$ is converted into the pure spin current I_s (see the inset), inducing local coherent magnetization auto-oscillations, which emit propagating coherent magnons into the surrounding $Bi YIG$ film.
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Figure 2
(a) Color-coded BLS intensity in the current-frequency coordinates measured by placing the probing spot in the middle of the $Pt$ line. f_A marks the frequency of SOT-induced auto-oscillations. (b) Representative BLS spectrum for I = 2.5 mA. (c) Current dependence of the peak BLS intensity. I_C marks the current corresponding to the onset of auto-oscillations. The data are obtained at H₀ = 2.0 kOe.
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Figure 3
(a) Color-coded spatial map of the BLS intensity recorded by rastering the probing laser spot over a 20 × 7 µm² area. Dashed lines show the contours of the $Pt$ line. (b) The x-coordinate dependence of the integrated BLS intensity on a log-linear scale. Symbols, experimental data; solid curves, exponential fit at |x| > 2 µm. Vertical dashed lines show the boundaries of the $Pt$ line. (c) Temporal dependences of the BLS intensity recorded at x = 0 and 10 µm. Dashed vertical lines mark the beginning of the rear edge of the pulses used to determine the magnon propagation delay. The data are obtained at H₀ = 2.0 kOe and I = 2.5 mA.
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Figure 4
(a) Calculated dispersion curves for magnons propagating parallel (ϕ = 0°) and perpendicular (ϕ = 90°) with respect to the direction of the static magnetic field. The dashed horizontal line marks the experimentally determined frequency of the auto-oscillations f_A. (b) Isofrequency curve at frequency f_A in the k_x-k_y coordinates, where k_x and k_y are the x and y components of the total wavevector k. (c) Calculated angular dependences of the wavelength and the group velocity of magnons at frequency f_A. The calculations are performed for H₀ = 2.0 kOe with use of the independently determined effective field of PMA, H_a = 1.84 kOe.
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Figure 5
(a) Field dependence of the experimentally determined magnon propagation length and of the imaginary part of the magnon wavevector k″. Symbols, experimental data; solid line, linear fit of the data for k″. The data are obtained at I = 2.5 mA. (b) Field dependence of the auto-oscillation onset current. Symbols, experimental data; solid line, linear fit.
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