Influence of the doping on the time-dependent magnetic behaviour of fine particles

Time dependent magnetic phenomena are analysed by measuring the changes of magnetization with time in the presence of a constant field on fine particles containing various percentage of dopants. The samples analysed are: iron oxides (Co-doped), CrO/sub 2/ (Fe/Sb- and Ir-doped) and Ba ferrite (Co/Ti-doped) particles. The doping causes a large increase of the coefficient S which characterizes the magnetic viscosity, and an increase of the thermal fluctuation field H/sub f/. The "activation volume" V/sub ac/, which is considered as the region of greatest magnetic instability in the particle and the "switching volume" V/sub c/ decrease with doping. These effects are principally attributed to the increase of the anisotropy directions distribution inside the particles and to the evolution of the magnetization reversal mode in the modified particles.<
>