Microscopic ESR study of N@C$_{60}$ using a Magnetic Resonance Force Microscope

We report electron spin resonance studies of the endohedral fullerene N@C$_{60}$ using the novel technique of magnetic resonance force microscopy (MRFM). These studies are performed at temperatures down to 1 K on both thin films of N@C$_{60}$ and in samples where the endohedral fullerene is incorporated into a bulk crystalline matrix\footnote{B. Naydenov, C. Spudat, W. Harneit, H. I. Suss, J. Hullinger, J. Nuss, M. Jansen, Chem. Phys. Lett., 424, 327 (2006)}. Utilizing the large magnetic field gradients ($\sim$ 10$^5$ Tesla/meter) in the vicinity of our micromagnetic probe tip, we are able to selectively probe the electron spins in sub--micron volumes. Further, our schemes for spin manipulation allow us to measure the spin--lattice relaxation rate (T$_1^{-1}$) with a spatial resolution in one dimension of approximately 20 nanometers. We will also discuss our efforts to improve the sensitivity of our microscope for detecting {\em individual} electronic spins.