Nano-granular FePt thin films for thermally-assisted magnetic recording

In order to extend the data storage density in hard disk drives beyond 1 Tb/in$^2$, nano-size grains of a high crystalline anisotropy ($K_u$) material are required to obtain these high densities and maintain thermal stability. A promising approach to recording using high-$K_u$ materials is thermally-assisted magnetic recording (TAR), in which the media is locally heated above the Curie temperature while a magnetic field is applied in order to write a bit. FePt with L1$_0$ crystalline order is a potential candidate for TAR media. We deposit FePt nano-granular films with carbon as the segregant material, by co-sputtering on glass substrates at elevated temperature. Underlayer materials are selected for heat-sinking and to attain high out-of-plane L1$_0$ order. Characterization of the media by x-ray diffraction, magnetometry and transmission electron microscopy show that we can achieve properties that are promising for TAR media, such as an average grain size $<$ 7.5nm, size distribution as low as 16\%, coercivity as high as 5 tesla and $K_u >$ 4.5 x 10$^7$ erg/cm$^3$. Recording densities exceeding 600 Gb/in$^2$ have been demonstrated for our FePt granular films using a static tester.