Phase transitions in systems with finite number of atoms

Properties of nanoparticles have been studied within the framework of Ising model and the method of random-field interactions: the average magnetic moment and position of critical points of the magnetic and the concentration phase transitions depending on their size. It is shown that the Curie temperature is inversely proportional to the size of the particle. Critical concentration of the ordered state decreases with increasing of size of nanoparticles until the percolation threshold of massive particles.