THERMOMAGNETIC WRITING AND TIME RESOLVED IMAGING IN A [Tb(7.9 Å) / Fe(11 Å)]20 MULTILAYER.

The origin of the thermomagnetic writing of information bits in magnetooptical recording media is not completely solved. The formation of magnetic bubbles during or after the short time local heating of the medium by a focussed laser beam is not yet well understood. Precise time resolved measurements and corresponding calculations are still chalenging. The difficulty of the data analysis comes mainly because thermal and magnetic experimental length scales are of the order of the light wavelength. We present here coupled nanosecond time resolved measurements of the heat diffusion and of the writing process in a Tb/Fe multilayer with a compensation point below room temperature. This enables us to deduce the spatio-temporal variation of the temperature and to prove that the formation of the magnetic bubble occurs during the cooling of our sample. A good fit of our thermal data can only be obtained if the thermal conductivity of our magnetic multilayer is supposed to be more than one order of magnitude smaller than the bulk alloy conductivity.