Programme Pavle Savic 2014: Self Assembly of Magnetic Hard-Spheres: Effect of Magnetic Field and Confinement 
Bilateral project with France 

Self-assembly of magnetic particles and multiple ways in which they can be manipulated have always attracted interest due to appearance of order from disorder. The applications of such systems are numerous. For example, self-assembly in binary mixtures of magnetic nano-particles can lead to lead to very strong magnets [H. Zeng et al., Nature 420, 395 (2002); D. J. Sellmyer, Nature 420, 374 (2002)]. In biology, there are magnetotactic bacteria whose dynamics is particularly sensitive to the presence of an external magnetic field and microstructures that they form can be manipulated by external magnetic field [R. Blakemore, Science 190, 377 (1975); E. Alphandery et al., ACS Nano 3, 1539 (2009)]. The two research groups will explore following three topics in the framework of the bilateral project: i) self-assembly of magnetic beads in the presence of an external magnetic field, ii) Microstructures of magnetic beads confined in two dimensions (eg. by gravity) in the presence of an external magnetic field, and iii) Mixture of binary magnetic beads with and without external magnetic field. The project represent a formalization of the fruitful collaboration between French and Serbian research groups that had already started. Until now, we were interested in the structures of lowest energy (ground state) of magnetic beads in the absence of an external magnetic field. A transition between three types of the structures has been identified with increasing number of the magnetic beads N. For small N (N<4), the short chains are ground states of the beads. For an intermediate number of beads (3< N <14), the rings are ground states with magnetization vectors forming a loop. Finally, for sufficiently large N (N> 13), the ground state structure is formed by the stack of the rings [R. Messina, L. Abou Khalil and I. Stankovic, Phys. Rev. E 89 (2014) 011202(R)].