  We study the thermodynamic properties of spin chains of Haldane-Shastry type
associated with the A_{N-1} root system in the presence of a uniform external
magnetic field. To this end, we exactly compute the partition function of these
models for an arbitrary finite number of spins. We then show that these chains
are equivalent to a suitable inhomogeneous classical Ising model in a spatially
dependent magnetic field, generalizing the results of Basu-Mallick et al. for
thezero magnetic field case. Using the standard transfer matrix approach, we
are able to compute in closed form the free energy per site in the
thermodynamic limit. We perform a detailed analysis of the chains'
thermodynamics in a unified way, with special emphasis on the zero field and
zero temperature limits. Finally, we provide a novel interpretation of the
thermodynamic quantities of spin chains of Haldane-Shastry type as weighted
averages of the analogous quantities over an ensemble of classical Ising
models.
