American Journal of Physics
An impressive demonstration of magnetism can be accomplished by placing some metal paperclips on a horizontal surface and then applying a vertical magnetic field. As the field is increased, the paperclips suddenly jump up, do a little dance, and then stand at attention. This behavior is related to the more common demonstration of paramagnetic and diamagnetic materials, which consists of hanging a small aluminum (paramagnetic) or glass (diamagnetic) cylinder horizontally in a strong horizontal magnetic field. A paramagnetic cylinder aligns its axis parallel to the applied field while a diamagnetic cylinder aligns its axis perpendicular to the field. This paper investigates these demonstrations by analyzing a magnetic spheroid in a uniform external field. Although this analysis explains the behavior of the paperclips, it predicts that both paramagnetic and diamagnetic cylinders will align themselves parallel to a uniform external field, in contrast to the common demonstration experiment.
Jackson, David P. "Dancing Paperclips and the Geometric Influence on Magnetization: A Surprising Result." American Journal of Physics 74, no.4 (2006): 272-279. https://aapt.scitation.org/doi/10.1119/1.2173279