Spin-current manipulation of photoinduced magnetization dynamics in Ta/CoFeB based nanostructures

Spin currents offer a way to control static and dynamic magnetic properties, and therefore they are crucial for next-generation MRAM devices or spin-torque oscillators. Manipulating the dynamics is especially interesting within the context of photo-magnonics. In typical 3d transition metal ferromagnets like CoFeB, the lifetime of light-induced magnetization dynamics is restricted to about 1 ns, which e.g. strongly limits the opportunities to exploit the wave nature in a magnonic crystal filtering device. Here, we report on the potential of spin-currents to increase the spin wave lifetime in a simple trilayer system, consisting of a heavy metal (8 nm of β-Tantalum (Platinum)), 5 nm CoFeB, capped by 3 nm Ruthenium. The samples were grown in UHV by magnetron sputtering (Ta, CoFeB) and E-beam evaporation (Pt, Ru), and subsequently patterned into micron-sized conduction strips using E-beam-lithography. Due to the spin Hall effect, the heavy metal layer generates a transverse spin current when a lateral charge current passes through the strip. Using time-resolved all-optical pump-probe spectroscopy, we investigate how this spin current affects the magnetization dynamics in the adjacent CoFeB layer. By analyzing the Kittel mode's frequency as a function of the charge current, we determine how Joule-heating affects the saturation magnetization. Furthermore, from extracting the current dependence of the effective Gilbert damping parameter, we have found Spin Hall angles of Θ
_Ta
= -0.043(11) for Ta and Θ
_Pt
= 0,086(12) for Pt. While such results can also be obtained from more established methods like BLS or ST-FMR, the benefit of our experimental approach lies in the possibility to investigate (sub-) picosecond dynamics. For instance, a look at the sub-picosecond timescale demonstrates that also the physics of ultrafast demagnetization can be manipulated by spin currents. The authors acknowledge financial support of the Deutsche Forschungsgemeinschaft within CRC 1073.