Force-gradient detected nuclear magnetic resonance

We have detected nuclear magnetic resonance in GaAs by selectively inverting 71Ga spins to create a local force gradient which shifts the mechanical resonance frequency of a nearby magnet tipped microcantilever. Employing a low spring constant cantilever (60 μN/m) at 4.4 K and 7 T, we demonstrate a magnetic moment sensitivity of 7.5×10−21 J/T, equal to the Curie Law magnetization from 7.1×108 71Ga spins. The method obviates the need to spin-lock sample magnetization during detection, allowing the signal to be collected for a time approaching the full spin-lattice relaxation time.