Figure 1

Scanning electron microscope image of the sample along with a schematic configuration used for the measurements. The detection of the vortex excitation was performed by resistance measurements with a lock-in technique (223 Hz and current $I_{\mathrm{mes}}=15\mu \mathrm{A}$) under the application of an ac excitation current $I_{\mathrm{exc}}=3\times {10}^{11}\mathrm{A}/{\mathrm{m}}^2$.Reuse & Permissions

Figure 2

(a) Time evolution of the vortex under the ac current application. The magnetization direction $\mathit{m}=(m_x,m_y,m_z)$ inside the dot on the $xy$ plane was obtained by micromagnetic simulation. The 3D plots indicate $m_z$ with the $m_x\mathrm{\text{−}}{m}_y$ vector plots superimposed. The plot on the left represents the initial state of the vortex core situated at the center of the dot with $r=410\mathrm{nm}$. The 3D plots on the right show the vortex on the steady orbital at $t=80.6$, 81.5, and 82.3 ns after applying the ac current ($f_0=380\mathrm{MHz}$ and $J_0=3\times {10}^{11}\mathrm{A}/{\mathrm{m}}^2$). These plots are close-ups of the square region around the dot center indicated by the black square in the plot on the left. The time evolution of the core orbital from $t=0$ to 100 ns is superimposed only on the $t=82.3\mathrm{ns}$ plot. (b) Time evolutions of the vortex core displacement ($x$) for three excitation frequencies $f=250$, 340, and 380 MHz ($r=410\mathrm{nm}$ and $J_0=3\times {10}^{11}\mathrm{A}/{\mathrm{m}}^2$). (c) Radius of the steady orbital as a function of the frequency for the dots with $r=410$, 530, and 700 nm.Reuse & Permissions

Figure 3

(a) Results of magnetoresistance measurements at room temperature for the dot with $r=700\mathrm{nm}$. The red (blue) line is the result for $H\parallel I$ ($H\perp I$). The results are plotted as a deviation in resistance ($\Delta R_{\parallel }$ and $\Delta R_{\perp }$) from the state in the zero magnetic field where the core exists at the center of the dot. The spin structure in the dot for each state (at $\pm 150\mathrm{Oe}$ denoted by the solid circles), which was determined by micromagnetic simulation, is also indicated. (b) $|\Delta R_{\parallel }|-|\Delta R_{\perp }|$ as a function of the magnetic field.Reuse & Permissions

Figure 4

(a) Experimental detection of the current-driven resonant excitation of a magnetic vortex core. The resistances are indicated as a function of the frequency of the ac excitation current for the dots with three different radii $r=410$, 530, and 700 nm. (b) Radius dependence of the resonance frequency. The blue rectangles and the red circles indicate the simulation and the experimental results, respectively. The experimental results for 8 samples are plotted. The red dashed line is the averaged value of the experimental data.Reuse & Permissions