FIELD-INDUCED OSCILLATION AND ROTATION OF DIAMAGNETIC OXIDE CRYSTALS

The harmonic oscillations of large diamagnetic mineral samples induced by a magnetic field is reported, for single crystals of quartz, corun dum, and calcite. It was seen for the first time that the period of os cillation, tau, was proportional to the reciprocal of the magnetic fie ld, H, where the restoring force of the string suspending the crystal became negligible in the high magnetic field. Accordingly, the value o f diamagnetic anisotropy, DELTA(chi), could be measured from the tau - H curve with a sensitivity of 5 x 10(-10) emu/cc. The DELTA(chi) valu es were 5.50 x 10(-9) emu/cc for quartz, 4.20 x 10(-9) emu/cc for coru ndum, 9.9 x 10(-8) emu/cc for calcite, and 8.8 x 10(-8) emu/cc for pol ycrystalline talc piled with the (001) planes aligned parallel. Signif icant field-induced rotations were observed for the suspended crystals . When the field was applied along the direction of the ''diamagnetic hard axis'' of the stationary crystal, the crystal gradually rotated w ith increasing field, so that the direction of the hard-axis was perpe ndicular to the applied field. The field-induced energy has a the maxi mum value when the field is applied along the diamagnetic hard axis. T his reorientation of the crystal occurs because the torque due to the field-induced anisotropic energy exceeds that of the restoring force i n high magnetic fields.