  Spin is an intrinsically quantum property, characterized by angular momentum.
A change in the spin state is equivalent to a change in the angular momentum or
mechanical torque. This spin-induced torque has been invoked as the intrinsic
mechanism in experiments ranging from the measurements of angular momentum of
photons g-factor of metals and magnetic resonance to the magnetization reversal
in magnetic multi-layers A spin-polarized current introduced into a nonmagnetic
nanowire produces a torque associated with the itinerant electron spin flip.
Here, we report direct measurement of this mechanical torque and itinerant
electron spin polarization in an integrated nanoscale torsion oscillator, which
could yield new information on the itinerancy of the d-band electrons. The
unprecedented torque sensitivity of 10^{-22} N m/ \sqrt{Hz} may enable
applications for spintronics, precision measurements of CP-violating forces,
untwisting of DNA and torque generating molecules.
