Nuclear magnetic resonance force microscopy: adiabaticity, external field effects, and demonstration of magnet-on-oscillator detection with sub-micron resolution

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2003

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Miller, Casey William

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Investigations of the adiabatic condition governing nuclear magnetic resonance force microscopy (NMR-FM) have been performed. It has been determined that the adiabatic conditional factor for protons in ammonium sulfate must have a value of 1.5 or greater to optimize the NMR-FM signal. A theoretical formalism is presented that describes the data. The characteristics of CoPt-capped single-crystal-silicon micro-oscillators with a magnetic field applied perpendicular to the magnetic film have been determined. The resonance frequency of the oscillators show two distinct regimes, one of softening and one of stiffening of the oscillator. A model is developed to describe the previously unseen softening. This work suggests that using NMR-FM with a magnetic particle on the oscillator is experimentally feasible. Magnet-on-oscillator NMR-FM has been demonstrated for the first time with our NMR-FM microscope using resonance slice thicknesses as small as ∼150 nm. The sample investigated was a semi-infinite slab of ammonium sulfate. The resonance slice of the microscope was scanned from vacuum into the sample by changing the tuned carrier frequency of the AC magnetic field H1. The resulting signal-to-noise ratio of ∼ 4 is slightly better than what was expected from conservative calculations. Finally, feasibility calculations and an experimental plan are set forth for the future measurement of relaxation times of single crystals of the superconductor magnesium diboride.

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