Sub-surface imaging with the magnetic resonance force microscope

The magnetic resonance force microscope (MRFM) is based on mechanical detection of magnetic resonance signals. The force between the field gradient due to a small permanent magnet and the spin magnetization in the sample is used to drive the oscillation of a high Q, low spring-constant micro-mechanical resonator (e.g. atomic force microscope cantilever). This same field gradient also enables microscopic magnetic resonance imaging. We will discuss the characteristics and capabilities of the electron spin MRFM we have fabricated. Our MRFM has a sensitivity of 3×10¹¹ electron spins at room temperature in an applied field of 253 Gauss. Its vertical resolution is 1 micron. One- and two-dimensional scans of a particle beneath the silicon cantilever have been performed which demonstrate the sub-surface spatial imaging capabilities. We also discuss recent advances in the miniaturization of two crucial MRFM components: the micromechanical resonator and the micromagnetic tip.