  We demonstrate theoretically that by placing a ferromagnetic particle between
a nitrogen-vacancy (NV) magnetometer and a target spin, the magnetometer
sensitivity is increased dramatically. Specifically, using materials and
techniques already experimentally available, we find that by taking advantage
of the ferromagnetic resonance the minimum magnetic moment that can be measured
is smaller by four orders of magnitude in comparison to current
state-of-the-art magnetometers. As such, our proposed setup is sensitive enough
to detect a single nuclear spin at a distance of $30$~nm from the surface
within less than one second of data acquisition at room temperature. Our
proposal opens the door for nanoscale NMR on biological material under ambient
conditions.
