Thermal stability in magneto-optical recording media: Analysis of magnetization decay

Thermal stability of amorphous TbFeCo monolayers and (TbFeCo/Pt) multilayers is studied by magnetic viscosity measurements M(t). Using, isothermal remanence measurements the relationship between the magnetization reversal process and its time dependence has been investigated. The non-linear evolution of magnetization with ln(time) happens when the mechanism responsible for magnetization reversal process is mainly domain nucleation. On the other hand domain wall motion process induces a linear M(t) behavior. For multilayers with very small Pt thickness (samples with high square hysteresis loop), magnetization time decay can be described easily by a single energy barrier E-B model. As Pt thickness increases, distribution of E-B becomes wider leading to almost linear magnetization decay with In(time) as in longitudinal recording media. The activation volume is determined for these media and shows a strong correlation with reversing field, thus yielding variations of stability over a written bit.