Magnetic dissipation and fluctuations in individual nanomagnets measured by ultrasensitive cantilever magnetometry

Cantilever magnetometry with moment resolution better than 10(4) mu (B) was used to study individual nanomagnets. By using the fluctuation-dissipation theorem to interpret measurements of field-induced cantilever damping, the low frequency spectral density of magnetic fluctuations could be determined with resolution better than 1 mu (B) Hz(-1/2). Cobalt nanowires exhibited significant magnetic dissipation and the associated magnetic fluctuations were found to have 1/f frequency dependence. In individual submicron rare-earth alloy magnets, the dissipation/fluctuation was very small and not distinguishable from that of a bare silicon cantilever.