The influence of shape anisotropy on the microstructure of magnetic dipolar particles

Abstract

In the first part of the present contribution we study theoretically the ground states of magnetic rods and ellipsoids with point dipoles. We consider two different orientations of dipoles: the dipole moment oriented along the short axis of the anisotropic particle and the dipole moment aligned along the long axis. We show that depending on the particle asphericity the ground states of ellipsoids and rods might be a chain and a ring (daisy) in two dimensions, or a carpet and a bracelet in three dimensions. If the ellipsoids or rods with the dipole moment coaligned with the long axis are elongated enough, the head-to-tail configuration of moments becomes less favourable than the antiparallel side-by-side pair of dipoles. This structural crossover in the ground state drives crucial changes in the microstructure of systems of anisotropic particles when the thermal energy starts being comparable to that of the interparticle interaction. We investigate the latter regime in the second part of our manuscript and provide a detailed analysis of the interparticle correlations using molecular dynamics simulations. We extensively study the influence of aspect ratios and different dipolar strengths on the structural properties, internal pressure and initial susceptibility of anisotropic particles' systems. We conclude that the particle shape anisotropy could be effectively used as a control parameter for the system microstructure.