Spin and Charge Pumping and Spin Wave Emission by Magnetic Domain Wall Annihilation: Quantum-Classical Micromagnetics Approach

Recent experiments on magnetic domain wall collisions [1] showed their importance in generating short-lived spin wave bursts, low-power signals which can be used in future spintronics devices. Using a new, time-dependent method to propagate the non-equilibrium density matrix (the TD-NEGF method) combined with the classical Landau-Lifshitz-Gilbert (LLG) equation [2], we analyze spin and charge currents produced by an annihilation of two colliding domain walls in a magnetic material coupled to two electron reservoirs. The advantage of this approach is in its self-consistent coupling between quantum electron spin and classical magnetic moments which gives rise to a dynamical Gilbert damping and allows for calculation of the exact charge current pumped out of the system, in contrast to an approximate solution given by the perturbative spin motive force formula combined with the LLG equation [3]. The pumped currents provide enough information to indirectly determine details of the annihilation event.

[1] S. Woo, T. Delaney, and G. S. D. Beach, Nature Physics 13, 448 (2017).
[2] M. D. Petrović, B. S. Popescu, U. Bajpai, P. Plechac, and B. K. Nikolić, arXiv:1802.05682 (2018).
[3] U. Bajpai, and B. K. Nikolić, arXiv:1810.11016 (2018).