Effective mass anisotropy o measured on a microcrystal by means of miniaturized torque magnetometry

Torque magnetization measurements on a Hg(Formula presented)(Formula presented)(Formula presented)(Formula presented) microcrystal of mass (Formula presented) ng were performed using a miniaturized torque sensor (120×90×4 μm) with a very high sensitivity of (Formula presented) N m. In an applied field of 1 T this allows the measurement of magnetic moments as small as (Formula presented) A (Formula presented), which is far beyond the sensitivity of the best commercial superconducting quantum interference device magnetometers. From the angle-dependent torque measurements an effective mass anisotropy of (Formula presented) and an estimate of the in-plane coherence length of (Formula presented) nm are extracted for Hg(Formula presented)(Formula presented)(Formula presented)(Formula presented). The large value of (Formula presented) reflects the quasi-two-dimensional nature of the mercury based cuprates and demonstrates the importance of vortex fluctuations in these materials. © 1996 The American Physical Society.