Magnetic dimer at a surface: Influence of gravity and external magnetic fields
Université de Lorraine, Laboratoire de Physique et Chimie Théoriques, LPCT - UMR CNRS 7019, 1 Boulevard Arago, 57070, Metz, France
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Accepted: 17 June 2020
Published online: 9 July 2020
The interaction of two dipolar hard spheres near a surface and under the influence of gravity and external perpendicular magnetic fields is investigated theoretically. The full ground-state phase diagram as a function of gravity and magnetic field strengths is established. A dimer (i.e., two touching beads) can only exist when the gravity and magnetic field strengths are simultaneously not too large. Thereby, upon increasing the magnetic field strength, three dimeric states emerge: a lying state (dimer axis parallel to the substrate), an inclined state (intermediate state between the lying and standing ones) and a standing state (dimer axis normal to the substrate). It is found that the orientation angles of the dimer axis and the dipole moment in the newly discovered inclined phase are related by a strikingly simple Snell-Descartes-like law. We argue that our findings can be experimentally verified in colloidal and granular systems.
Key words: Soft Matter: Colloids and Nanoparticles
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature, 2020