First, a brief review of thermal decay of magnetization is given. Discussions on activation volume are presented in detail for longitudinal recording media. It is noted that the activation volume estimated based on waiting time methods is found to decrease with increasing reversing field for all the media under consideration. This result suggests that an activation volume in a written bit changes from place to place, depending upon on stray field due to a bit-transition. The recording noise is closely related to activation volume as well. Thermal stability of amorphous TbFeCo mono-layers 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 is investigated. The non-linear evolution of magnetization with In(time) takes place 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 by a single energy barrier E_B model. As Pt thickness increases, the distribution of E_B becomes wider leading to almost linear magnetization decay with In(time) as in longitudinal recording media. Finally, the life time of written domains is discussed in terms of domain size. It is concluded that the difference between a pinning field and wall-field is a decisive factor for governing a life time.
展开▼
