Force-detected ESR from E$^\prime$ centers

Magnetic Resonance Force Microscopy (MRFM) is a novel technique that combines magnetic resonance with scanned probe techniques. We report on low temperature force-detected electron spin resonance (ESR) signals from $E^\prime$-centers in fused silica (SiO$_2$). By utilizing the high gradients close to a micron sized SmCo ferromagnetic tip mounted on an AFM cantilever, spin resonance was observed from a sub- micron thick ``sensitive slice'' whose location can be varied with respect to the sample surface. E$^\prime$ centers at low temperatures ($<$ 10 K) are characterized by long spin-lattice relaxation times T$_1$ approaching a few seconds. The spins were adiabatically inverted at the appropriate frequency by means of microwave FM techniques and T$_1$ was studied as a function of field gradient. We also discuss the sensitivity of the microscope and ongoing efforts to improve it.