MEASUREMENT OF THE DYNAMICS OF THE MAGNETIZATION REVERSAL INDIVIDUAL SINGLE-DOMAIN CO PARTICLES

The first magnetization measurements of individual single-domain particles (50-150 nm) patterned by electron-beam lithography are presented. The angular dependence of the switching field is measured and the temperature dependence (0.1-6 K) of the reversal process is investigated by two independent methods: (i) by measuring the switching field and the width of the switching field distribution as a function of temperature and field sweeping rate, (ii) by measuring the probability for switching at constant applied magnetic field as a function of time and temperature. We found that mean values like the mean switching field and the mean switching time verify a simple model based on thermal activation between 1 and 6 K. Below 1 K thermal activation is not sufficient anymore to explain their variation. However the width of the switching field distribution and the probability of switching are in disagreement with such a model. The results are discussed in view of Macroscopic Quantum Tunnelling of magnetization.