Rotational Stability of a Diamagnetic Rod

When Faraday identified/named diamagnetism (relative permeability μ < 1) in 1845, he reported in Arts. 2253-2260 of [1] that a glass rod would align itself at right angles to the lines of magnetic field of his laboratory electromagnet. He also noted in Art. 2269 that such object moved “into the positions of weakest magnetic action.” Faraday’s test objects were suspended from a string, but W. Thomson [5, 6] (at age 23) soon noted that it should be possible to levitate diamagnetic objects, although he speculated that the magnetic force would be too weak for such levitation to be observed in practice. Diamagnetic levitation was first observed in 1939 [7]. See also [8, 9, 10, 11, 12, 13]. A superconductor can be regarded as an extreme form of diamagnetism, with relative permeability μ = 0; levitation of a superconductor was first observed in 1945 [14, 15]. A recent example of diamagnetic levitation of a graphite rod has been given in [16, 17], in which the magnetic field was provided by a pair of cylindrical magnets, each with horizontal (diametric) magnetization, perpendicular to the axes of the cylinders, as illustrated below (PDL = parallel dipole line).