  We study the low-temperature thermodynamic properties of a number of
frustrated quantum antiferromagnets which support localized magnon states in
the vicinity of the saturation field. For this purpose we use 1) a mapping of
the low-energy degrees of freedom of spin systems onto the hard-core object
lattice gases and 2) an exact diagonalization of finite spin systems of up to
N=30 sites. The considered spin systems exhibit universal behavior which is
determined by a specific hard-core object lattice gas representing the
independent localized magnon states. We test the lattice gas description by
comparing its predictions with the numerical results for low-lying energy
states of finite spin systems. For all frustrated spin systems considered we
find a strong variation of the low-temperature specific heat passing the
saturation field and a maximum in the isothermal entropy at saturation field
resulting in an enhanced magnetocaloric effect.
