  The thermodynamics of a site-diluted ferromagnetic Heisenberg model for spin
$S=1/2$ with interaction anisotropy in spin space is investigated. The study is
aimed at presenting the magnetocaloric properties of such a model, including
the entropy and temperature changes in magnetization/demagnetization processes,
generalized Gr\"uneisen ratio as well as the quantities characterizing the
efficiency of magnetic cooling cycles. The results are obtained using Pair
Approximation (PA) method and extensively compared with the Molecular Field
Approximation (MFA) calculations. The importance of interaction anisotropy and
site-dilution is discussed. The inadequacy of the MFA approach (even on the
qualitative level) is found for selected quantities, while PA provides the
results which are consistent with the experimentally observed behaviour.
