# Transient spin dynamics in a single-molecule magnet

## TL;DR

This paper investigates the validity of semi-classical spin equations in single-molecule magnets, comparing different approximation schemes and revealing limitations in describing transient spin dynamics.

## Contribution

It derives a generalized spin equation of motion with non-local time dependence and compares it to simplified models, highlighting their applicability and limitations.

## Key findings

- Transient dynamics are absent in the time-independent parameter model.
- The time-dependent parameter model breaks down under strong coupling.
- The generalized equation captures non-local temporal effects.

## 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) time-dependent, 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.