Magnetic dimer at a surface: Influence of gravity and external magnetic fields

Area of Science:

• Physics
• Soft Matter Physics
• Colloidal Science

Background:

• Dipolar hard spheres near surfaces are fundamental in soft matter.
• External fields (gravity, magnetic) significantly influence particle interactions and self-assembly.

Purpose of the Study:

• To theoretically investigate the ground-state phase diagram of two interacting dipolar hard spheres near a surface.
• To characterize the emergent dimeric states under combined gravity and magnetic fields.

Main Methods:

• Theoretical investigation of interacting dipolar hard spheres.
• Establishment of the ground-state phase diagram.
• Analysis of dimeric states and their orientations.

Main Results:

• A dimer exists only when gravity and magnetic field strengths are simultaneously moderate.
• Three dimeric states are identified: lying, inclined, and standing.
• A Snell-Descartes-like law governs the orientation angles in the inclined phase.

Conclusions:

• The study establishes a comprehensive phase diagram for dipolar hard spheres under external fields.
• A novel inclined dimeric state and its unique orientational law are discovered.
• Findings are relevant for experimental verification in colloidal and granular systems.