Vortex Polarity Switching by a Spin-Polarized Current

The spin-transfer effect is investigated for the vortex state of a magnetic nanodot. A spin current is shown to act similarly to an effective magnetic field perpendicular to the nanodot. Then a vortex with magnetization (polarity) parallel to the current polarization is energetically favorable. Following a simple energy analysis and using direct spin-lattice simulations, we predict the polarity switching of a vortex. For magnetic storage devices, an electric current is more effective to switch the polarity of a vortex in a nanodot than the magnetic field.

Figure 1

Schematic of the heterostructure.

Figure 2

The energy of the vortex (9) for three different fields: $m_0=0$ (left panel), $m_0=-0.2$ (middle panel), and $m_0=-0.5$ (right panel). The cutoff parameter $\lambda =0.264a$ and $\ell =2.89a$. The switching occurs for $m_0\approx -0.47$.

Figure 3

Amplitude of $S_z(t)$ at the vortex center from numerical simulations on a square lattice with circular boundary of diameter $L=200a$. Other parameters of the system: $\eta =0.25$, $\epsilon =0.01$, $\delta =0.03$; time is measured in units of $\hslash /J$. The critical current $j\approx -0.0033$.