Granular L10 FePt:X (X = Ag, B, C, SiOx, TaOx) thin films for heat assisted magnetic recording

Abstract

Ordered L10 FePt thin films are of interest as potential Heat Assisted Magnetic Recording media. In order to achieve the microstructure and magnetic properties to support recording at densities beyond 1 Tbit/in2, it is necessary to add segregants into the FePt films. In this work, the effects of a number of segregants, X, on the microstructure and magnetic properties of FePt:X (X = Ag, B, C, SiO x , TaO x ) thin films, deposited by RF sputtering with various volume content (0–50%), various in-situ heating temperatures (450–600 °C), various Ar pressures (10–40 mtorr) and various sputtering powers (25–200 W) onto 1′′ Si substrates with a MgO texture (002) underlayer (20 nm), were investigated. It was observed that introducing segregants (B, C, SiO x , and TaO x ) into the FePt reduced ordering and grain size of the FePt:X thin films. Ag was found to offset the reduction of ordering in the FePt:X films. The B, SiO x and TaO x promoted columnar growth whereas C promoted a secondary nucleation layer but produced the least reduction of ordering. By varying the volume content of the segregants, the grain size of the FePt:X can be controllably reduced throughout the 2.5–10 nm range. It was found that TaO x produced the best exchange decoupling, thermal durability, grain isolation and hindered grain coalescence as compared with the films deposited with B, C or SiO x . With the FePt:C:Ag films sputtered at 450 °C, a perpendicular coercivity measured at room temperature as high as 25 kOe was achieved; whereas with B, SiO x , and TaO x , perpendicular coercivities as high as 11 kOe were obtained. These FePt:X thin films with small grain size, columnar microstructure and high coercivity are believed to be favorable for application in Heat Assisted Magnetic Recording. The role of surface energies of FePt and the segregant in columnar growth of FePt grains is discussed.