Magnetic ghosts and monopoles

Abstract

While the physics of equilibrium systems composed of many particles is well known, the interplay between small-scale physics and global properties is still a mystery for athermal systems. Non-trivial patterns and metastable states are often reached in those systems. We explored the various arrangements adopted by magnetic beads along chains and rings. Here, we show that it is possible to create mechanically stable defects in dipole arrangements keeping the memory of dipole frustration. Such defects, nicknamed 'ghost junctions', seem to act as macroscopic magnetic monopoles, in a way reminiscent of spin ice systems.

Elastic properties of magnetosome chains

“…Thus, for sufficiently large N the interaction between the dipoles with i = 1 and i = N overcompensates the effect of bending. This crude estimate indicates that the closed ring is the minimal energy configuration for chains of five or more particles, while a comparison of the exact energies for the linear chain and the closed ring (plotted in figure 5) shows that this is true for chains with four or more particles, as has already been shown in several earlier studies [17,[42][43][44][45]. We also note that the closed ring configuration with tangential orientation of the magnetization has been demonstrated experimentally using electron holography for cobalt nanoparticles [46].…”

Assembly of magnetic spheres in strong homogeneous magnetic field

“…By essence, the dipole-dipole driving force for selfassembly is long range and highly anisotropic (i.e., noncentral pair potential) [10,11] and therefore represents a formidable theoretical challenge. In this spirit, the pioneering theoretical work of Jacobs and Beans [12] and later that of de Gennes and Pincus [13] about the microstructure of self-assembled (spherical) magnets shed some light on the ordering mechanisms.…”

Magnetoelastic instability in soft thin films

“…The dipoles tend to form chains along the field orientation. These chains possess their own elastic behavior due to the magnetism [9][10][11][12]. This orientation effect is understood by considering the magnetic potential energy of both dipoles…”

“…Of course, a more elaborated model can be proposed to capture the details of the film behavior. However, it should be based on the multiple interactions between many dipoles leading to complex theoretical developments as found recently for chains of magnets [9][10][11][12]. When the field strength becomes more important, the system may jump from one minimum to a neighboring one, explaining the abrupt modification of the equilibrium angle and the jump at some φ value, as seen in Figure 3(b).…”