Active microlevers as miniature torque magnetometers

An extremely sensitive miniature torque magnetometer using Si p-doped piezoresistive cantilevers is described. The magnetization m+(Combining right arrow above sign) of very small magnetic or superconducting samples (≤1 μg) deposited on the cantilever can be measured via the torque τ+(Combining right arrow above sign)=m+(Combining right arrow above sign)×B+(Combining right arrow above sign) produced on them by an applied field B. The high resolution in the lever deflection of the order of 0.1 Å corresponds to a torque sensitivity of the order of Δτ≃10-14 Nm. In a homogeneous field of 1 T this device allows magnetic moments as small as Δm≃10-14 Am2 to be measured, a value far smaller than that measurable by the best commercial superconducting quantum interference device magnetometers. Measurements performed on microcrystals of the high-Tc superconductors Bi2Sr2Ca1Cu2O8 and Hg1Ba2Ca3Cu4O10 in the static and dynamic modes demonstrate the excellent performance of this device at low temperature and in magnetic fields ranging between a few mT and 5 T. © 1996 American Institute of Physics.