Thermal field fluctuations in a magnetic tip/implications for magnetic resonance force microscopy

Thermally excited magnetic fluctuations are fundamental to the behavior of small ferromagnetic particles and have practical consequences for the propo sed detection of individual spins by magnetic resonance force microscopy (M RFM). In particular, fluctuating fields from a nearby magnetic tip can incr ease the relaxation rate of spins in a sample if there is significant spect ral density of field fluctuation at the Larmor frequency of the target spin . As an initial step toward understanding this issue, magnetic field fluctu ations have been simulated which emanate from a magnetic tip with dimension s 60 nmx60 nmx2 mu m. It was found that the fluctuations in a cobalt magnet ic tip were too strong for MRFM experiments aimed at detecting individual e lectron spins. However, the results obtained for a PrFeB tip fell within th e tolerance required. (C) 2000 American Institute of Physics. [S0021-8979(0 0)81308-0].