Manipulating Spins by Cantilever Synchronized Frequency Modulation: A   Variable Resolution Magnetic Resonance Force Microscope
  We report a new spin manipulation protocol for periodically reversing the sample magnetization for Magnetic Resonance Force Microscopy. The protocol modulates the microwave excitation frequency synchronously with the position of the oscillating detection cantilever, thus allowing manipulation of the spin magnetization independent of both magnetic field gradient strength and cantilever response time. This allows continuous variation of the detected sample volume and is effective regardless of spin relaxation rate. This enhanced flexibility improves the utility of MRFM as a generally applicable imaging and characterization tool. 
K.C. Fong, P. Banerjee, Yu. Obukhov, D.V. Pelekhov and P.C. Hammel