  Magnetic systems can be described by the classical Landau-Lifshitz (LL)
equation or the fully quantum open Heisenberg model. Using the Lindblad master
equation and the mean-field approximation, we demonstrate that the open
Heisenberg model is reduced to a generalized LL equation. The open dynamic is
modeled using spin-boson interactions with a common bosonic reservoir at
thermal equilibrium. By tracing out the bosonic degrees of freedom, we obtain
two different decoherence mechanisms: on-site dissipation and an effective
spin-spin interaction mediated by bosons. Using our approach, we perform
hysteresis calculations, closely connected with the Stoner-Wohlfarth theory. We
compare the exact numerical master equation and the mean-field model, revealing
the role of correlations originated by non-local interactions. Our work opens
new horizons for the study of the LL dynamics from an open quantum formalism.
