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Current-driven dynamics of noncollinear magnetization textures and thereby induced spin and charge pumping: A multiscale quantum-classical approach 
Thursday, 11 July 2019,  3:00
To Friday, 12 July 2019
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Current-driven dynamics of noncollinear magnetization textures and thereby induced spin and charge pumping: A multiscale quantum-classical approach

Prof. Branislav K. Nikolic, Full Professor of Physics, University of Delaware, USA

This talk introduces recently developed [1,2] multiscale and self-consistent computational tool which combines time-dependent nonequilibrium Green function (TDNEGF) algorithms, scaling linearly in the number of time steps and describing quantum-mechanically conduction electrons in the presence of time-dependent fields of arbitrary strength or frequency, with classical description of the dynamics of local magnetic moments based on the Landau-Lifshitz-Gilbert (LLG) equation. Such TDNEGF+LLG approach can be applied to a variety of problems where current-driven spin torque induces the dynamics of magnetic moments as the key resource for next generation spintronics. Previous approaches for describing such nonequilibrium many-body system have neglected noncommutativity of quantum Hamiltonian of conduction electrons at different times and, therefore, the impact of time-dependent magnetic moments on electrons which can lead to pumping of spin and charge currents that, in turn, can self-consistently affect the dynamics of magnetic moments themselves including introduction of non-Markovian damping and magnetic inertia terms into the LLG equation [2]. Thus, TDNEGF+LLG can be viewed as “quantum-classical micromagnetics” which captures numerous effects missed by widely utilized purely classical micromagnetics. We use examples of current- or magnetic-field-driven motion of domain walls within magnetic nanowires (including their annihilation observed in very recent experiments [3]) to illustrate novel insights that can be extracted from TDNEGF+LLG simulations. In particular, TDNEGF+LLG as a nonperturbative (i.e., numerically exact) framework allows us to establish the limits of validity of simpler theories, such as the so-called spin-motive force theory [4] for pumped charge current by time-dependent noncollinear and noncollinear magnetic textures which turns out to be just the lowest order of the result predicted by TDNEGF+LLG.

REFERENCES: [1] M. Petrović, B. S. Popescu, U. Bajpai, P. Plecháč, and B. K. Nikolić, Phys. Rev. Applied 10, 054038 (2018). [2] U. Bajpai and B. K. Nikolić, Phys. Rev. B 99, 134409 (2019). [3] S. Woo, T. Delaney, and G. S. D. Beach, Nat. Phys. 13, 448 (2017). [4] S. E. Barnes and S. Maekawa, Phys. Rev. Lett. 98, 246601 (2007).

Location ICN2 Seminar Hall, ICN2 Building, UAB
Contact This email address is being protected from spambots. You need JavaScript enabled to view it.
https://icn2.cat/en/events/eventdetail/1114/current-driven-dynamics-of-noncollinear-magnetization-textures-and-thereby-induced-spin-and-charge-pumping-a-multiscale-quantum-classical-approach

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