Magnetic Orientation under Gravity:  Biphenyl and Naphthalene Crystals

Abstract

The crystal growth has been investigated in horizontal and vertical magnetic fields of 80 kOe. The crystallographic axes have been determined by X-ray diffraction and compared with the magnetic axes. Biphenyl and naphthalene crystals are diamagnetic (χ 2 < χ 3 < χ 1 ) and plate-shaped. They grow with the normal to the plate at a fixed angle (16° for biphenyl and 21° for naphthalene), i.e., with the χ 1 axis parallel, to magnetic fields. For the phenomenon a plausible explanation is proposed in terms of the potential energy in magnetic and gravitational fields. The magnetic energy has a minimum, but the gravitational energy does not, in the direction that the χ 1 axis is along magnetic fields. The magnetic torque may compete with the gravitational torque, and crystals of certain dimensions may be stabilized in this direction against a gravitational field.