High-gradient nanomagnet-on-cantilever fabrication for scanned probe detection of magnetic resonance

Magnetic resonance force microscopy (MRFM) is a non-invasive, three-dimensional imaging technique that employs attonewton-sensitivity cantilevers to mechanically detect the interaction between the field gradient of a magnetic particle and magnetically-active sample spins. Achieving high sensitivity demands the use of a high field gradient. In order to study a wide range of samples, it is equally desirable to locate the magnetic tip on the cantilever.;The work in this thesis centers on the development of nanomagnets on cantilevers that produce sufficiently large field gradients for nanometer-scale nuclear spin MRFM imaging and single electron spin detection. A new fabrication protocol is introduced to prepare nickel and cobalt nanomagnets on cantilevers. Custom attonewton-sensitivity cantilevers were batch fabricated. Nanomagnets were prepared separately on micrometer-scale silicon chips using electron beam lithography and electron beam deposition. Each magnet-tipped silicon chip was serially attached to a cantilever using focused ion beam manipulation. Frequency-shift cantilever magnetometry and superconducting quantum interference device magnetometry were used to assess the nanomagnet magnetization. X-ray photoelectron spectroscopy was used to determine the extent of oxidation damage.;A cobalt nanomagnet-tipped chip attached to an attonewton-sensitivity cantilever was used to detect statistical fluctuations in the proton magnetization of a polystyrene film. MRFM signal was studied versus rf irradiation frequency and tip-sample separation. The tip-field gradient ∂ Btipz /∂z of the nanomagnet was estimated to be between 4.4 and 5.4 MTm-1, which is comparable to the gradient used in recent 4 nm resolution 1H imaging experiments and nearly an order of magnitude larger than the gradients achieved in prior magnet-on-cantilever MRFM experiments. These magnet-tipped cantilevers are projected to achieve a proton imaging resolution of 5 to 10 nm.;The key design considerations and development of a new magnetic resonance force microscope are also discussed in this thesis. The microscope will use the newly-developed nanomagnet-tipped cantilevers to conduct high-resolution, three-dimensional MRFM imaging experiments at cryogenic temperatures, in high vacuum, and at magnetic fields up to 9 T.;Overall, the work in this thesis has significantly advanced the capabilities of MRFM and has poised the field to begin conducting high-resolution imaging experiments on a broad range of previously-inaccessible samples.