  A gravitational model of magnons in thermal equilibrium with a ferromagnetic
spin chain is developed in a phenomenological bottom-up approach. A large
Schwarzschild-AdS black hole background is used as the thermal reservoir and
the magnon dynamics is obtained by scalar fields and branes in the bulk. The
key feature of this model is that the coupling of the spin chain is related
with the radial position in which the brane is located. We further study a
ferromagnetic spin chain with a competing interaction and find that the
couplings are related by the difference of positions of the branes. We show how
to obtain the model from a weak limit of a dynamical gravitational system. This
allows us to embed the model into a holographic system. The couplings can be
related to entanglement entropy at finite temperature of the CFT since the
turning point of minimal surfaces coincides with the position of the branes.
The difference of entropy is used to define a notion of distance between the
chain couplings.
