Probing magnetization dynamics in individual magnetite nanocrystals using magnetoresistive scanning tunneling microscopy

The magnetization dynamics of individual magnetite nanocrystals was probed by variable-temperature magnetoresistive scanning tunneling microscopy, in which a magnetoresistive junction is formed between the substrate and the magnetic particle under study. By tuning the temperature close to the magnetization blocking of a superparamagnetic particle, the slow magnetization switching of the particle caused fluctuations in the tunnel current passing through the particle, which appeared as telegraph noise in current vs time measurements. Analysis of the current fluctuations yielded estimates for the low local magnetic field sensed by the particle, its magnetic anisotropy energy, and the low limit for the spin-polarization degree of the nanocrystals, which for some particles appeared to be as high as 90%.