  Magnetic torque is used to actuate nano-torsional resonators, which are
fabricated by focused-ion-beam milling of permalloy coated silicon nitride
membranes. Optical interferometry is used to measure the mechanical response of
two torsion modes at resonance, which is proportional to the magnetization
vector of the nanomagnetic volume. By varying the bias magnetic field, the
magnetic behavior can be measured with excellent sensitivity ($\approx 10^8
\mu_B$) for single magnetic elements.
