High Sensitivity Magnetic Resonance Force Microscopy

We report high sensitivity detection of electron spin resonance from E$\,^\prime$ centers in fused silica using the Magnetic Resonance Force Microscope. Operating at low temperatures and with high magnetic field gradients in the 2--3 G/nm range, we easily observe magnetic resonance signals from less than 1000 $\mu_B$, and signal averaging enables detection of less than 100 $\mu_B$ with a spin sensitivity of 10 $\mu_B$. While $T_1$ at low temperatures is approximately 5 sec, the lifetime of the magnetization under conditions of periodic adiabatic reversal is considerably shorter and is observed to be of order 100 ms. We will discuss design features necessary to operate the microscope at millikelvin temperatures.