Geometric Structure of an Aqueous Solution of Paramagnetic Nanoparticles in the Presence of a Magnetic Field

Computer simulation of two-dimensional colloidal systems, in which interactions between particles are induced and controlled by an external rotating magnetic field, has been performed. The effective interaction potential of particles, along with the conventional pair potential, includes also three-particle interaction. It is shown that one of the parameters of the potential—field precession angle—radically changes the character of particle interaction and the phase diagram. In particular, at small angles the system behaves like a two-dimensional system with a purely repulsive soft-disk potential, whereas at large angles it behaves like a generalized Lennard-Jones system with the (nm)-potential; the presence of the three-particle part of potential reduces the temperature of the gas–liquid critical point. At intermediate field precession angles the phase diagram contains melting lines of triangular crystals of high and low density, between which a phase with a Kagome lattice was found. Our results serve an important guide for future experiments and simulation of colloidal systems, as well as for solving many problems in the fields of “soft” matter, physical chemistry, chemical physics, photonics, and materials science