Axisymmetric scalable magneto-gravitational trap for diamagnetic particle levitation.

We report on the design, construction, and use of axisymmetric magnetic traps for levitating diamagnetic particles. The magnetic traps each consist of two pole pieces passively driven by a neodymium iron boron (NdFeB) permanent magnet. The magnetic field configuration between the pole pieces combined with the earth's gravitational field forms a 3D confining potential capable of levitating a range of diamagnetic substances, e.g., graphite powder, silica microspheres, and gallium nitride (GaN) powder and nanowires. Particles trap stably at atmosphere and in high-vacuum for periods up to weeks with lifetimes largely determined by choices made to actively destabilize the trap. We describe the principles of operation, finite element design, approximate closed-form results for design rules, and examples of operation of such traps.