DYNAMICAL MEASUREMENT OF DOMAIN-WALL NUCLEATION AND ANNIHILATION IN INDIVIDUAL AMORPHOUS CO PARTICLES

We present magnetization measurements of individual amorphous Co parti cles (300 nmx200 nmx30 nm) patterned by electron-beam lithography. The hysteresis loops show mainly two magnetization jumps corresponding to domain-wall nucleation and annihilation. The angular dependence of th ese magnetization jumps is measured and the temperature dependence (0. 1-6 K) of the nucleation and the annihilation processes is investigate d by two independent methods: switching field and switching time measu rements. Finally we compare the results obtained on one particle with those of an array of about 2x10(7) particles. We show experimentally t hat the dynamical properties measured on individual particles are conn ected with an unusual 1/T relaxation of the array of particles.