Transient spin dynamics in a single-molecule magnet

Abstract

We explore the limitations and validity of semi-classically formulated spin equations of motion. Using a single-molecule magnet as a test model, we employ three qualitatively different approximation schemes. From a microscopic model, we derive a generalized spin equation of motion in which the parameters have a non-local time-dependence. This dynamical equation is simplified to the Landau-Lifshitz-Gilbert equation with i) timedependent, and ii) time-independent parameters. We show that transient dynamics is essentially non-existing in the latter approximation, while the former breaks down in the regime of strong coupling between the spin and the itinerant electrons.

Time-retarded damping and magnetic inertia in the Landau-Lifshitz-Gilbert equation self-consistently coupled to electronic time-dependent nonequilibrium Green functions

“…Nevertheless, in the limit [34,60] of weak electronspin/local-magnetic-moment interaction [i.e., small J sd in Eqs. (4) and (5)] one can derive analytically a type of generalized LLG equation [34][35][36][37] for each local magnetic moment which is next approach in the hierarchy that sheds light onto different effects included in the numerically exact TDNEGF+LLG scheme. Instead of the conventional Gilbert damping term in Eq.…”

“…Although quantum-classical approaches which automatically include time-retardation effects have been discussed previously [6,22,[34][35][36][37], they have been focused on the simples examples where one or two local magnetic moments (pertinent to, e.g., magnetic molecules) interact with either closed electronic quantum system [22,35] (i.e., not attached to macroscopic reservoirs to allow electron spin and charge currents to flow into and from an FIG. 1.…”

“…Schematic view of two-terminal devices where an infinite 1D TB chain, describing electrons quantum-mechanically, is attached to two macroscopic reservoirs while its middle part hosts: (a) single local magnetic moment, initially oriented in the +x-direction, placed in an external magnetic field pointing along the +z-direction; (b) 11 local magnetic moments (illustration shows 7 of them), initially oriented in the +xdirection, placed in an external magnetic field pointing along the +z-direction; (c) three-site-wide head-to-head magnetic DW whose motion is driven by an external magnetic field pointing in the +x-direction. Electrons within 1D TB chain and classical local magnetic moments interact via the s-d exchange coupling of strength J sd , and classical local magnetic moments within the DW in (c) additionally interact with each other via the Heisenberg exchange coupling of strength J. external circuit), or open electronic quantum system but employing approximations [6,34,36,37] to obtain analytical solution. Thus, these approaches are not suitable for simulations of spintronic devices containing large number of noncollinear local magnetic moments.…”

Charge Transport and Entropy Production Rate in Magnetically Active Molecular Dimer

“…[53][54][55][74][75][76]. This field provides a torque on the loclized spin, however, only when the spin-degeneracy is broken in the current.…”

Nonlinear spin torque, pumping, and cooling in superconductor/ferromagnet systems

“…In such systems charge and (non-collinear) spin transport are closely linked and need to be treated on the same footing. Recently there has also been increased interest to couple superconductors to magnets and find out how superconductivity affects the magnetization dynamics, [5][6][7][8][9][10][11][12][13][14][15] including thermally driven effects [16]. On the other hand, recent work has shown that a combination of magnetic and superconducting systems results to giant thermoelectric effects [17][18][19][20] coupling charge and heat currents.…”