Magnetic orientation under gravity: Biphenyl and naphthalene crystals

The crystal growth has been investigated in horizontal and vertical magnetic fields of XO kOe. The crystallographic axes have been determined by X-ray diffraction and compared with the magnetic axes. Biphenyl and naphthalene crystals are diamagnetic (chi(2) < chi(3) < chi(1)) and plate-shaped. They grow with the normal to the plate at a fixed angle (16 degrees for biphenyl and 21 degrees for naphthalene), i.e., with the chi(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 chi(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.