Active microlevers as miniature torque magnetometers

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Abstract
An extremely sensitive miniature torque magnetometer using Si p‐doped piezoresistive cantilevers is described. The magnetization m↘ of very small magnetic or superconducting samples (≤1 μg) deposited on the cantilever can be measured via the torque τ↘=m↘×B↘ 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.