Field-induced oscillation and rotation of diamagnetic oxide crystals

Abstract

The harmonic oscillations of large diamagnetic mineral samples induced by a magnetic field is reported, for single crystals of quartz, corundum, and calcite. It was seen for the first time that the period of oscillation, τ, was proportional to the reciprocal of the magnetic field, H, where the restoring force of the string suspending the crystal became negligible in the high magnetic field. Accordingly, the value of diamagnetic anisotropy, Δϰ, could be measured from the τ — H curve with a sensitivity of 5 × 10−10 emu/cc. The Δϰ values were 5.50 × 10−9 emu/cc for quartz, 4.20 × 10−9 emu/cc for corundum, 9.9 × 10−8 emu/cc for calcite, and 8.8 × 10−8 emu/cc for polycrystalline talc piled with the (001) planes aligned parallel. Significant 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 with increasing field, so that the direction of the hard-axis was perpendicular to the applied field. The field-induced energy has a the maximum value when the field is applied along the diamagnetic hard axis. This reorientation of the crystal occurs because the torque due to the field-induced anisotropic energy exceeds that of the restoring force in high magnetic fields.