Current Controlled Spin Reversal of Nanomagnets with Giant Uniaxial Anisotropy

Since a giant magnetic anisotropy of 9 meV per atom has been realized on a Pt surface, we use the kinetic Monte Carlo method to study the spin dynamics of a nanomagnet that is made by putting a line of such adatoms on a thin metallic strip so that the fixed spins are coupled very weakly and a spin-polarized current can be injected into the strip. There is a magnetization hysteresis versus the current because of the giant anisotropy. The hysteresis loop is diminished exponentially with the temperature increasing. The magnetization can be controlled by injecting a spin-polarized current.

Figure 1

A demonstration of the nanomagnet consisting of a metallic substrate (or overlayer, shadow part) and some adatoms (or particles, circles). The upper one is the top view and the lower one the side view.

Figure 2

The dependence of normalized magnetization on the electronic currents with the spin polarizations: (a) $p=1$ (averaged over 600 runs) and (b) $p=0.75$ (averaged over $5\times 120$ runs). The temperature is 30 K.

Figure 3

Temperature dependence of coercive currents $I_c$ with $p=1$ (averaged over 400 runs). The anisotropy parameter $K_u^A$ is 12 and 6 meV for the two curves.

Figure 4

Time dependence of normalized magnetization simulated using full polarization $p=1$ and four temperatures: (a) $T=40$, (b) $T=70$, (c) $T=80$, and (d) $T=110\mathrm{K}$. Three currents 0.00 759 (lower), 0.01 265 (middle), and 0.024 (upper) $\mu \mathrm{A}$ are used for every panel. The solid lines are fitted using Eq. (3).

Figure 5

Saturated magnetization $m_s$ (a), and parameters $t_0$ (b) and $b$ (c) defined in Eq. (3) as functions of temperature. The other parameters are the same as those of Fig. 4. The lines in (a) and (b) are fitted using Eq. (4).

Figure 6

Saturated magnetizations as functions of the current for 40, 70, 80, and 110 K. The other parameters are the same as those for Fig. 4. The solid lines are linear fittings to the data.