Random Spin Signal in Magnetic Resonance Force Microscopy

We study a random magnetic resonance force microscopy (MRFM) signal caused by the thermal vibrations of high frequency cantilever modes in the oscillating cantilever-driven adiabatic reversals (OSCAR) technique. We show that the regular MRFM signal with a characteristic decay time, $\tau_m$, is followed by a non-dissipative random signal with a characteristic time $\tau_r$. We present the estimates for the values of $\tau_m$ and $\tau_r$. We argue that this random MRFM signal can be used for spin detection. It has a ``signature'' of a sharp peak in its Fourier spectrum.