MAGNETIZATION STABILITY AND INTERACTIONS IN PARTICULATE RECORDING MEDIA

The basic magnetic properties of fine particles used in magnetic recording media are studied. The examined materials are alpha-Fe metal, iron oxide (pure and Co-doped), chromium dioxide (pure and Ir- or Fe/Sb-doped) and barium ferrite (pure and Co/Ti-doped) particles. The magnetostatic interactions among the particles are analysed with the evaluation of the remanence curves. In metal particles the different roles of positive and negative interactions are investigated and the results are interpolated to the condition of 'zero' interactions. In the other particles the ionic additions weaken the interaction strength. The time-dependent magnetic behaviour is evaluated with measurements of magnetization decay and subsequent deduction of magnetic viscosity, fluctuation field and activation volume. The time effects are found to be related both to the interparticle interactions which reduce the magnetic viscosity and to the presence of substituting ions which lower the thermal stability of the magnetization. These results are discussed in correlation with the evolution of the magnetization switching mode of the particles induced by the interactions and by the ionic additions in the crystal structure.