Magnetic resonance force detection using a membrane resonator

Silicon nitride (Si$_3$N$_4$) membranes are commercially-available, versatile structures that have a variety of applications. Although most commonly used as the support structure for transmission electron microscopy (TEM) studies, membranes are also ultrasensitive high-frequency mechanical oscillators. The sensitivity stems from the high quality factor $Q\sim10^6$, which has led to applications in sensitive quantum optomechanical experiments. The high sensitivity also opens the door to ultrasensitive force detection applications. We report force detection of electron spin magnetic resonance at 300 K using a Si$_3$N$_4$ membrane with a force sensitivity of 4 fN/$\sqrt{\mathrm{Hz}}$, and a potential low temperature sensitivity of 25 aN/$\sqrt{\mathrm{Hz}}$. Given membranes' sensitivity, robust construction, large surface area and low cost, SiN membranes can potentially serve as the central component of a compact room-temperature ESR and NMR instrument that has superior spatial resolution to conventional NMR.