Development of Magnet-on-Oscillator Low Temperature NMR Force Microscopy

We report recent advances for our nuclear magnetic resonance force microscopy (NMRFM) experiment. Force detection of nuclear spins is made possible by coupling NMR spin flip sequences to a mechanical oscillator. Periodic inversion of the spins in a magnetic field gradient provides the ac coupling force. The force sensitivity for NMRFM improves with decreasing distance between a small gradient magnet and the spins in a sample. Adapting a perpendicular oscillator orientation allows us to decrease the magnet-to-sample distance, providing increased sensitivity. We've also adapted a magnet-on-oscillator design. With this approach, we can perform experiments using oscillating cantilever-driven adiabatic reversal, a technique which has been used to detect single electron spins below the surface of a solid [1]. We've integrated an optical fiber interferometer to measure an oscillator's motion with sub nanometer precision. We can routinely measure the resonance frequencies, quality factors, and spring constants of various oscillators.\\[4pt] [1] Rugar D et al. Nature. 2004;430:329--332