Ultrafast demagnetization and damping in magnetic thin film heterostructures: critical role of spin-orbit coupling

Speaker: Prof. UAM dr hab. Bivas Rana

Affiliation: Institute of Spintronics and Quantum Information (ISQI), Faculty of Physics and Astronomy, Adam Mickiewicz University, Poznań

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Abstract:

A femtosecond pulsed laser beam can partially or fully demagnetize a magnetic material within sub-picosecond time scale [1] and thereby induce precessional dynamics of magnetization, which is damped in the nanosecond time scale. The ultrafast demagnetization not only offers to investigate the fundamental interaction of spins with orbital motion, charge and lattice, but also promise for the development of ultrafast data storage technology. The damping constant on the other hand, governs the performance of many spintronic devices. Therefore, the investigation of underlying mechanism and find out efficient ways to control these phenomena are crucial for future application point of view.

In this seminar I will discuss about our recent research on femtosecond pulse laser beam induced ultrafast demagnetization, remagnetization and damping of precessional magnetization dynamics in Si/SiO2-substrate/heavy-metal/Co20Fe60B20/MgO/Al2O3 heterostructures. Our research shows that the bulk spin-orbit coupling (SOC) strength of underlayer heavy-metal and SOC strengths at heavy-metal/Co20Fe60B20, Co20Fe60B20/MgO interface play a critical role in controlling ultrafast demagnetization, remagnetization times and the degree (i.e. percentage) of demagnetization [2]. We find an inverse correlation between these ultrafast times with the damping parameter albeit they occur in different time scale. Surprisingly, the damping constants in these multilayers show an anisotropic behavior with respect to the direction of in-plane orientation of magnetization, which originates from bulk SOC of ferromagnetic layer and anisotropic two-magnon scattering at the interface [3]. We further show that by doping Co20Fe60B20/MgO interface with suitable material with varying SOC strength it is even possible to control the damping constant.

References:

[1] E. Beaurepaire, J. C. Merle, A. Daunois, and J. Y. Bigot, “Ultrafast spin dynamics in ferromagnetic nickel”, Phys. Rev. Lett. 76, 4250 (1996).

[2] S. N. Panda, B. Rana, Y. Otani, and A. Barman, “Role of Spin–Orbit Coupling on Ultrafast Spin Dynamics in Nonmagnet/Ferromagnet Heterostructures”, Adv. Quantum Technol. 5, 2200016 (2022).

[3] B. Rana and Y. Otani, “Anisotropy of magnetic damping in Ta/CoFeB/MgO heterostructures”, Sci. Rep. 13, 8532 (2023).