  The magnetocaloric effect in a two-dimensional Ising model is considered for
different ratios between parameters of inter-site repulsion of nonmagnetic
impurities and exchange coupling. Classical Monte Carlo simulations on a square
lattice show that in case of weak coupling and at sufficiently high
concentrations of nonmagnetic impurities the long-range ferromagnetic ordering
breaks down to give isolated spin clusters in the ground state of the system.
This leads to appearance of a paramagnetic response in the system at the zero
temperature and nonzero entropy of the ground state. The feasibility to detect
frustration of ground state using data on the magnetic entropy variation is
discussed
