Coherent spin current amplification by a non-adiabatic interaction.

We propose a mechanism for coherent spin current amplification in a solid-state magnetic medium device. The mechanism relies on the non-adiabatic regime in a magnetic media [1-3], in which the energetic balance between a precessing magnetic moment and a driving ac spin current is interrupted. In this mechanism, optical pulses perturb a precessing magnetic moment in the presence of a driving ac field, thus injecting energy into the system. The injected energy manifests in spin pumping current, which coherently adds to the injected spin current.
We study the gain characteristics, saturation profile, phase relations between the driving ac spin current and spin pumping current , as well as the behavior of both small and large angle dynamical regimes which are excited by application of either weak or strong pulses. A comparison to the conventional optical amplifier is discussed. The mechanism we propose is a highly sensible magnetization controller, as well as a first step toward a practical spin current amplifier for spintronics applications.


[1] M. Brik, N. Bernstein, and A. Capua, ArXiv e-prints (2020).
[2] A. Capua, C. Rettner, S.-H. Yang, T. Phung, and S. S. P. Parkin, Nature Commun. 8, 16004 (2017).
[3] A. D. Karenowska et al., Physical Review Letters 108, 015505 (2012).