Control of propagating spin waves via spin transfer torque in a metallic bilayer waveguide

We investigate the effect of a direct current on propagating spin waves in a CoFeB/Ta bilayer structure. Using the micro-Brillouin light scattering technique, we observe that the spin-wave damping and amplitude may be attenuated or amplified depending on the direction of the current and the applied magnetic field. Our work suggests an effective approach for electrically controlling the propagation of spin waves in a magnetic waveguide and may be useful in a number of applications such as phase-locked nano-oscillators and hybrid information-processing devices.

Figure 1

Schematics of spin-polarized current generation in a bilayer and the experimental setup of micro-BLS.

Figure 2

SW amplitude as a function of dc and external magnetic field. Inset: A raw BLS spectrum showing both the Stokes and anti-Stokes peaks scattering from magnons.

Figure 3

Detailed analysis of data presented in Fig. 2. (a) Magnetic-field-dependent SW amplitude when dc's of opposite directions were applied. (b) Extracted $H_R$ as a function of dc. (c) Change in the propagating SW amplitude at a particular magnetic field as a function of dc obtained by subtracting SW amplitudes for dc's of opposite directions.

Figure 4

The change in decay rate (left axis) and damping constant (right axis) as a function of dc. The error bars quoted are for $\Delta \alpha$ and mainly arise from uncertainty in $\Delta A.$

Figure 5

BLS intensity as a function of the microwave power applied across the antenna for 8 mA (red crosses) and −8 mA (blue open circles) for (a) $H>0,$ (b) $H<0,$ and (c) $H<0$ from a CoFeB(10)/Ta(1) waveguide. The arrows refer to the microwave power used in other experiments presented in this paper. The insets illustrate the STT arising from the spin-polarized electrons $\mathit{\sigma }$ with $j>0$ for (a) $H>0$ and (b) $H<0$, respectively.