Competing spin transfer and dissipation at Co/Cu(001) interfaces on femtosecond timescales*

Spin dynamics driven by optical excitation with femtosecond (fs) laser pulses offers fascinating possibilities in the ultrafast manipulation of spin-dependent microscopic processes in magnetically ordered materials and heterostructures. In particular, fs spin currents are very promising for future ultrafast spintronics applications. However, the role of the interface in fs spin dynamics is to date largely unexplored. By means of a combined experimental-theoretical approach, we identify the fundamental microscopic processes during optically induced, fs charge and spin transfer at a model epitaxial ferromagnet/paramagnet interface for technologically relevant ferromagnetic heterostructures. A comparison of fs time-resolved, interface-sensitive magneto-optical experiments with ab initio time-dependent density functional theory on the Co/Cu(001) interface demonstrates that the ultrafast spin dynamics originates from spin-dependent charge transfer, including resonantly excited minority spin back-transfer from Cu to Co. Already on timescales below 100 fs, this fs spin transfer competes with dissipation of spin angular momentum mediated by spin-orbit coupling [1].

Reference:
[1] J. Chen, U. Bovensiepen, A. Eschenlohr, T. Mueller, P. Elliott, E. K. U. Gross, J. K. Dewhurst, and S. Sharma, http://arxiv.org/abs/1803.03090 (2018).