Columnar Structure in FePt–C Granular Media for Heat-Assisted Magnetic Recording

Abstract

We attempted a compositionally graded sputtering process to overcome the phase separation in the growth direction in the FePt–C granular film in order to realize the columnar structure of FePt grains with an aspect ratio larger than 1.5. In order to overcome the problem of the formation of a second FePt–C layer for the thickness larger than 6 nm, we deposited the FePt–C film by changing the carbon concentration during the sputtering process. The formation of the second FePt–C layer was suppressed, which led to the growth of columnar grains with an aspect ratio of 1.5. The overall volume fraction of carbon is a decisive factor on the size of the FePt grains. Using the compositionally graded process, FePt–C nanogranular films with an average grain size of 7.8 nm, a thickness of 10 nm, and a perpendicular coercivity of 40 kOe were obtained.