EXPERIMENTAL-EVIDENCE OF THE NEEL-BROWN MODEL OF MAGNETIZATION REVERSAL

Presented are the first magnetization measurements of individual ferro magnetic nanoparticles (15-30 nm) at very low temperatures (0.1-6 K). The angular dependence of the hysteresis loop evidenced the single dom ain character of the particles. Waiting time, switching field, and tel egraph noise measurements showed for the first time that the magnetiza tion reversal of a well prepared ferromagnetic nanoparticle can be des cribed by thermal activation over a single energy barrier as originall y proposed by Neel and Brown. The ''activation volume'' estimated by t hese measurements was close to the particle volume.