Ring-chain structural transitions in a ferromagnetic particles system induced by a dc magnetic field.

We carry out statistical analysis of cluster structures formed by ferromagnetic particles in a dc magnetic field based on a flexible chain model. In the absence of a magnetic field, ferromagnetic particles tend to form ring structures. When a dc magnetic field is applied, the rings are broken into chains if the intensity of the field is sufficiently high since the dipole moment of each particle is aligned in the field direction. We analyze the conditions under which ring-chain structural transitions occur and clarify the dependence of the probabilities of the creation of ring and chain structures on control parameters such as the strength of the dipole-dipole interactive energy between particles, the intensity of the magnetic field and the cluster size.