Nuclear magnetic resonance force microscopy of ammonium dihydrogen phosphate and magnetism of cobalt nanocrystals

A Nuclear Magnetic Resonance Force Microscopy (NMR-FM) technique utilizing a somewhat uncommon experimental geometry has been developed. Characterization of external field effects on soft permalloy micromagnets on double torsional oscillators was performed. We showed that at high enough fields (above 1 Tesla), the quality factor for each mode is comparable to the zero field value. The changes in resonance frequency fit well with our model, and permitted high-sensitivity magnetic moment and magnetic anisotropy measurement. Effects of laser power on cantilevers used for NMR-FM has been studied in detail. The origins of the observed self-sustained oscillations has been addressed by our model. NMR-FM detection has been shown in an ammonium dihydrogen phosphate sample. Imaging and spin manipulation techniques were used for the first time to detect the nuclear spins in a sample with short relaxation times. A magnetic study of epitaxially grown cobalt nanocrystals on a Si(111) substrate has been performed. Enhancement of the magnetic moment and anisotropy energy have been observed and data are consistent with single domain model. Experimental evidence indicates small inter-nanocrystal interactions. Finally, future directions in achieving the single-spin detection limit is addressed.