Ultrafast switching of antiferromagnets via spin-transfer torque

Picosecond switching of the staggered antiferromagnetic order is shown to be realizable through spin-transfer torques from a short current pulse. The coupled dynamics of sublattice magnetization is mapped onto a classical pendulum subject to gravity and a driving pulse, where switching occurs if the pendulum acquires sufficient kinetic energy during the pulse to overcome the maximum of the effective gravity potential. The optimal switching scheme is explored through the dependence of switch angle and magnetic loss on the duration and strength of the current pulse. The physics discussed here provides a general route towards multifunctional THz applications via the spin-transfer torque in antiferromagnetic materials.

Figure 1

For $\mathit{p}\parallel \widehat{\mathit{z}}$, an AF precession is implemented by the exchange torque, whereas a ferromagnetic precession resorts to the demagnetization field.

Figure 2

Effective model of the staggered field switching. (a) Perpendicular STTs cant ${\mathit{m}}_{1,2}$ slightly out of the basal plane. (b) By $\theta =2\varphi$, the switching is mapped onto a pendulum subjected to gravity, damping, and a driving torque. (c, d) Phase portraits of the pendulum for $\mathcal{T}=0$ and $\mathcal{T}>0$ (large enough to open up the attractor at origin), respectively.

Figure 3

Out-of-plane magnetization $\left(2m_z\right)$ and staggered field projected on the easy axis as functions of time in picoseconds. Pulse duration $T=10\mathrm{ps}$; STT strength ${\omega }_s=0.0034$; Gilbert damping $\alpha =0.005$. Parameters for NiO: ${\omega }_E/\left(2\pi \right)=27.4\mathrm{THz},{\omega }_a/\left(2\pi \right)=1\mathrm{GHz}$.

Figure 4

Upper left (right): Terminal angle of $\ell$ as a function of the pulse duration from 2 to 20 ps, and ${\omega }_s$ from 0.003 to 0.005 for $\alpha =0.005(\alpha =0.01)$. Lower left (right): Total magnetic loss due to Gilbert damping for $\alpha =0.005(\alpha =0.01)$.