  We theoretically study the randomly positioned two-dimensional system of
interacting magnetic dipoles representing the monolayer arrays of single-domain
particles. It is showed the onset of the dipolar in-plane superferromagnetic
ordering of Ising spins at the surface concentrations of nanoparticles above
0.24. The critical concentration of particles with random easy axis arrangement
at zero temperature is 0.65. It is demonstrated that the ensemble with Ising
arrangement of spins is ordered at high temperatures close to a particle Curie
point.
