Abstract
We investigate optically excited terahertz standing spin waves in noncollinear magnetic bilayers. Using femtosecond laser-pulse excitation, a spin current is generated in the first ferromagnetic (FM) layer, and flows through a conductive spacer layer to be injected into the second (transverse) FM layer, where it exerts a spin-transfer torque on the magnetization and excites higher-order standing spin waves. We show that the noncollinear magnetic bilayer is a convenient tool that allows easy excitation of terahertz spin waves, and can be used to investigate the dispersion and thereby the spin-wave stiffness parameter in the thin-film regime. This is experimentally demonstrated using wedge-shaped Co and CoB (absorption) layers. Furthermore, the damping of these terahertz spin waves is investigated, showing a strong increase of the damping with decreasing absorption layer thickness, much stronger than expected from interface spin pumping effects. Additionally, a previously unseen sudden decrease in the damping for the thinnest films is observed. A model for the additional damping contribution incorporating both these observations is proposed.
| Original language | English |
|---|---|
| Article number | 184439 |
| Number of pages | 6 |
| Journal | Physical Review B |
| Volume | 99 |
| Issue number | 18 |
| DOIs | |
| Publication status | Published - 28 May 2019 |
Funding
We thank Y. Tserkovnyak for valuable discussions. This work is part of the Gravitation program “Research Centre for Integrated Nanophotonics,” which is financed by the Netherlands Organisation for Scientific Research (NWO).