Control of Magnetic Fluctuations by Spin Current

We use microfocus Brillouin light scattering spectroscopy to study the interaction of spin current with magnetic fluctuations in a Permalloy microdisk located on top of a Pt strip carrying an electric current. We show that the fluctuations can be efficiently suppressed or enhanced by different directions of the electric current. Additionally, we find that the effect of spin current on magnetic fluctuations is strongly influenced by nonlinear magnon-magnon interactions. The observed phenomena can be used for controllable reduction of thermal noise in spintronic nanodevices.

Figure 1

(a) Schematic of the experiment. (b) Pseudocolor logarithmic map of the BLS intensity vs current and frequency. (c)–(e) Representative spectra acquired at $I=-26$, 0, and 26 mA, respectively. Curves are Lorentzian fits to the data.

Figure 2

(a) Normalized integral intensity under the peak (circles) and its inverse value (squares) vs current. The solid line is a linear fit to the data. (b) The peak central frequency (circles) and calculated effective magnetization normalized by its value at $I=0$ (squares) vs current. The inset shows the linewidth of the peak vs current.

Figure 3

Temporal evolution of the normalized effective magnetization (circles) and the normalized integral BLS peak intensity (squares) resulting from a $1\mu \mathrm{s}$-long pulse of current $I$ applied at $t=0$: (a) $I=25\mathrm{mA}$, (b) $I=-25\mathrm{mA}$, (c) $I=-30\mathrm{mA}$.

Figure 4

Calculated average fluctuation energy per mode at the labeled values of the strength of the spin transfer torque $\beta$ normalized by its critical value ${\beta }_c$. The spread in energy at a given frequency and $\beta$ is caused by the variations of the damping rates ${\Gamma }_i$ among different modes with the same frequency.