Current-Driven Vortex Oscillations in Metallic Nanocontacts

We present experimental evidence of subgigahertz spin-transfer oscillations in metallic nanocontacts that are due to the translational motion of a magnetic vortex. The vortex is shown to execute large-amplitude orbital motion outside the contact region. Good agreement with analytical theory and micromagnetics simulations is found.

Figure 1

(a) SEM and (b) AFM image of point contact. (c) Low-frequency PSD (power spectral density) measured at ${\mu }_{0}H=0.21\mathrm{T}$ for several applied currents. Inset of (c): CPW and applied field geometry.

Figure 2

(a) Color map of experimental PSD for ${\mu }_{0}H=350\mathrm{mT}$. Solid squares are results of micromagnetics simulations. (b) Top view of the vortex magnetization profile in the free layer obtained from simulation. (c) In-plane component of magnetization (black for $m_y=+1$ and white for $m_y=-1$) for the entire simulation area for $I=30\mathrm{mA}$. Also shown are the contact and the vortex orbit (158 nm in radius).

Figure 3

Vortex oscillation frequency as a function of (a) applied current and (b) applied field. Dots are experimental data, and solid lines are fits based on Eq. (4).