Theoretical investigation of new magnetic recording media using an energy landscape method
Magnetic material has played an important role in the information storage technology. We have worked out a phase diagram showing spin torque switching for perpendicular anisotropy media at nonzero temperature. A new area is predicted where the system can vibrate between precessional and parallel states quickly and therefore creates "telegraph" noise region. The result was later confirmed by a nanopillar experiment. The density of magnetic recording is restricted by the superparamagnetic limit. To overcome this limit people have used perpendicular recording to replace the traditional longitudinal recording and are working on other approaches to get over the superparamagnetic limit including heat assisted recording, patterned media and exchange coupled media. Anisotropy graded media provides an alternative solution to achieve high areal density while keeping the writing field relatively low and good thermal stability. A two-dimensional energy landscape of the switching of anisotropy graded media is calculated to give an intuitive way of understanding the switching, as well as a way to quantitatively calculate the switching rate by mapping the problem onto a one-dimensional Langevin random walk. Then an iterative algorithm of for finding the saddle point of the energy landscape, which we call barbell algorithm, is used to locate the saddle point and the whole switching trajectory.