Magnetic Fluctuations in Individual Superparamagnetic Particles

Fluctuations of the magnetic moment direction of single Fe
₃
O
₄
nanoparticles were measured by conductive atomic force microscopy. Superparamagnetic nanoparticles were deposited on an Fe-Pt thin film, and the current through the film and individual particles was detected as a function of time. Due to magnetoresistance in the particle-film system, changes in the particle moment direction lead to different current levels. The effect of magnetic fields between -69 and 153 Oe on the characteristic current levels was used to determine the effective anisotropy of the particle. Magnetoresistance values of 45% were observed.