Granular L10 FePt-B and FePt-B-Ag (001) thin films for heat assisted magnetic recording

A comparison was made of FePt-B and FePt-B-Ag thin films having different volume contents of boron, which were RF sputtered with in-situ heating at 425-575 deg. C onto Si substrates with 20 nm thick (002) MgO. By introducing boron into FePt and varying the sputtering conditions, films with grain sizes ranging from 2.5 to 10 nm were produced. The boron promoted columnar growth, but made ordering more difficult. However, by adding Ag into FePt-B, ordering improved while coercivity increased from 7 to 11 kOe with no significant impact on the microstructure. We obtained films with grain sizes down to 2.5 nm with center-to-center spacing of 3.1 nm. The reduced grain size, columnar microstructure and increase in ordering and coercivity by adding Ag into the FePt-B thin films are favorable for application in heat assisted magnetic recording.