  Kerr-Newman de Sitter (KNdS) spacetimes have a rich thermodynamic structure
that involves multiple horizons, and so differs in key respects from
asymptotically flat or AdS black holes. In this paper, we show that certain
features of KNdS spacetimes can be reproduced by a constrained system of $N$
non-interacting spins in a magnetic field. Both the KNdS and spin systems have
bounded energy and entropy, a maximum of the entropy in the interior of the
energy range, and a symmetry that maps lower energy states to higher energy
states with the same entropy. Consequently, both systems have a temperature
that can be positive or negative, where the gravitational temperature is
defined analogously to that of the spins. We find that the number of spins $N$
corresponds to $1/\Lambda$ for black holes with very small charge $q$ and
rotation parameter $a$, and scales like $\sqrt{(a^2+q^2)/\Lambda}$ for larger
values of $a$ and $q$. By studying constrained spin systems, we provide insight
into the thermodynamics of KNdS spacetimes and its quantum mechanical
description.
