  We demonstrate a novel method allowing the study of the magnetic state
dynamics of a single nanoparticle by means of electron transport measurements.
Elliptical 550 nm x 240 nm permalloy nanoparticles are wired with non-magnetic
leads for magnetotransport measurements in the presence of a radio-frequency
(RF) field. Their resistance exhibits sharp jumps due to the anisotropic
magnetoresistance even at room temperature. An RF field induces DC voltage
across the nanoparticle which can be partially depleted at a certain RF
frequency when a magnetic vortex core resonance is present. An application of
an additional DC magnetic field eliminates the vortex and reinstates the
unperturbed DC voltage level. The vortex core resonance frequencies are found
and the smallest resonance widths are estimated to be less than 6 MHz.
