Oscillator microfabrication, micromagnets, and magnetic resonance force microscopy

Abstract

We report our advances in nuclear magnetic resonance force microscopy (NMRFM) in three areas: 1) MEMS microfabrication studies of single-crystal-silicon mechanical oscillators using double-sided processing; 2) micromagnetometry, anisotropy, and dissipation studies of individual permalloy micromagnets on oscillators; and 3) mechanical-oscillator detection of NMR in the magnet-on-oscillator scanning mode. In the first area, we report details of our back-etch microfabrication process, and characterize oscillator resonant frequency, quality factor, and spring constant by measuring the noise spectral density of oscillator motion. In the second studies, we report changes in the resonant frequency and quality factor for each of four modes of our oscillators for two shapes and sizes of permalloy thin-film (~30 and 180~nm) micromagnets; a simple, quantitative model is used to describe both low-field softening and high-field stiffening. Finally, we report scanning-mode NMR force detection of an ammonium-sulfate single-crystal interface and a polymethyl-methyl-acrylate thin film at room temperature. These latter studies use 2-μm-radius permalloy magnets on silicon oscillators to image the NMR response from resonant volumes as small as 3 μm3. These NMRFM studies are the first reported that attain sub-micron resonant-slice resolution at room temperature.