External field effects on the resonant frequency of magnetically capped oscillators for magnetic resonance force microscopy

Abstract

We study the resonant frequency shift of CoPt-capped single-crystal-silicon micro-oscillators when a magnetic field is applied perpendicular to the magnetic film, as required for application to nuclear magnetic resonance force microscopy. The oscillator resonant frequencies show two distinct regimes of behavior. At low fields, when the magnetic moment is nearly perpendicular to the external field, the frequency decreases sharply with field, while at high fields, when the moment and field are nearly aligned, the frequency increases. We present models that accurately describe both behaviors. The transition point between these two regimes scales with the volume of the micromagnets.