Influence of the interparticle interaction of the ensemble of immobilized superparamagnetic ferroparticles on the static, magnetic and thermodynamic properties of the system

This paper presents a study of the effect of the interparticle dipole-dipole interaction on the static, thermodynamic, and magnetic properties of the ensemble of stationary superparamagnetic particles in the external magnetic field. The relaxation of the magnetic moment of the model ferroparticles occurred by the Néel mechanism. The directions of the easy axes of all particles were assumed to be parallel to each other, but at the angle to the direction of the external magnetic field. The direction of the easy axes was described using the polar and azimuth angles. The potential energy of the system includes a single-particle dipole-axial interaction, a single-particle dipole-field interaction and long-range interparticle dipole-dipole correlations. In the system, two variants of the distribution of ferroparticles over the volume of the container are considered: in the nodes of a simple cubic lattice and randomly. The described model is studied theoretically by expanding the Helmholtz free energy into a classical virial series up to the second virial coefficient. Using the new theory, the contribution of dipole-dipole interactions in the changes in the magnetic susceptibility, magnetization, and heat capacity of the system is estimated, and the results are represented graphically. Important information necessary to the development and synthesis of new magnetic materials with controlled properties is provided.