  Multi-level magnetic recording is a new concept for increasing the data
storage capacity of hard disk drives. However, its implementation has been
limited by a lack of suitable media capable of storing information at multiple
levels. Herein, we overcome this problem by developing dual FePt-C nanogranular
films separated by a Ru-C breaking layer with a cubic crystal structure. The
FePt grains in the bottom and top layers of the developed media exhibited
different effective magnetocrystalline anisotropies and Curie temperatures. The
former is realized by different degrees of ordering in the L10-FePt grains,
whereas the latter was attributed to the diffusion of Ru, thereby enabling
separate magnetic recordings at each layer under different magnetic fields and
temperatures. Furthermore, the magnetic measurements and heat-assisted magnetic
recording simulations showed that these media enabled 3-level recording and
could potentially be extended to 4-level recording, as the up-down and down-up
states exhibited non-zero magnetization.
