Time-Dependent Density Functional Theory for Spin Dynamics
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With the development of ultrashort sub-picosecond laser pulses, the last two decades have witnessed the emergence of a new field of magnetism, namely, femtomagnetism. This consists of controlling the magnetic interactions by using purely optical stimuli at sub-picosecond timescales, where both the exchange interaction and the magnetic anisotropy cannot be considered constant. The modeling of such phenomena is at present populated by semiempirical theories, which heavily rely on assumptions about the dominant interactions responsible for the dynamics and the system intrinsic properties (e.g., the conductivity). However, in the last few years, there have been a few attempts to look at the problem from a purely ab initio point of view, namely, by using time-dependent density functional theory. Here we will review the progress in this field and show how a theory not biased by assumptions can shed light into the fundamental aspects of the laser-induced magnetization dynamics. In particular we will discuss the ultrafast demagnetization of transition metals both in their cluster and bulk form and the possibility of spin transfer between sublattices in compounds containing magnetic ions. The chapter is also complemented by a short review of time-dependent spin density functional theory in the context of spin dynamics.
This work (MS, JS, and SS) was supported by Science Foundation Ireland (Grants No. 14/IA/2624 and No. 16/US-C2C/3287). We gratefully acknowledge the Irish Centre for High-End Computing (ICHEC) for the provision of computational facilities. We also acknowledge the Trinity Centre for High Performance Computing (TCHPC) for use of computational resources. SS would like to thank DFG for funding through TRR227.
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