Effective mass anisotropy of HgBa2Ca3Cu4O10 measured on a microcrystal by means of miniaturized torque magnetometry.

Abstract

Torque magnetization measurements on a Hg${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{10}$ microcrystal of mass $m\ensuremath{\simeq}380$ ng were performed using a miniaturized torque sensor (120\ifmmode\times\else\texttimes\fi{}90\ifmmode\times\else\texttimes\fi{}4 \ensuremath{\mu}m) with a very high sensitivity of $\ensuremath{\Delta}\ensuremath{\tau}\ensuremath{\simeq}{10}^{\ensuremath{-}14}$ N m. In an applied field of 1 T this allows the measurement of magnetic moments as small as $m={10}^{\ensuremath{-}14}$ A ${\mathrm{m}}^{2}$, which is far beyond the sensitivity of the best commercial superconducting quantum interference device magnetometers. From the angle-dependent torque measurements an effective mass anisotropy of $\ensuremath{\gamma}=\sqrt{\frac{{m}_{c}^{*}}{{m}_{\mathrm{ab}}^{*}}}=52(1)$ and an estimate of the in-plane coherence length of ${\ensuremath{\xi}}_{\mathrm{ab}}=1.8(5)$ nm are extracted for Hg${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{10}$. The large value of $\ensuremath{\gamma}$ reflects the quasi-two-dimensional nature of the mercury based cuprates and demonstrates the importance of vortex fluctuations in these materials.