Zero field viscosity in perpendicular media

Summary form only given. The thermal relaxation of magnetic media is a topic of considerable importance. The stability is typically characterized by measuring the time dependence of the coercivity or by measuring the magnetization decay rate as a function of applied reverse field. For large thermal stability factors (KV/kT), the magnetization decay in zero applied field is considered to be negligible. This is not necessarily the case, however, in state-of-the-art media with KV/kT less than 100. We have recently reported on measurements of the decay of remanence in zero applied field for a series of longitudinal thin film and particulate media and for self-assembled L1/sub 0/ FePt nanoparticles. Here we report on the measurement and calculation of zero-field relaxation in a film with perpendicular anisotropy. For illustration we have used a CoCrPtB film with a coercivity of 1900 Oe. The decay of magnetization was measured at zero applied field after the application of a saturation-reverse field sequence for different reverse fields and the initial viscosity coefficient, S/sub 0/ = dm/dlog(t), was measured as a function of the initial remanent magnetization.