Analysis of grain size in FePt films fabricated using remote plasma deposition

Highlights: • XRD and TEM analysis of grain size on L1₀ ordered films has been performed. • The approach does not allow material properties to be controlled. • There is no correlation between target DC bias voltage and the grain size. • Desirable small grains with a narrow grain size distribution are not produced. - Abstract: Remote plasma sputtering (RPS) offers a high degree of control over the sputtering parameters used to deposit thin metallic films and has demonstrated a capability to control the media grain size distribution. Narrow grain size distributions remain a key requirement for future magnetic media. Here we report a comprehensive magnetometry, X-ray diffraction and transmission electron microscopy study of how RPS affects the grain size distribution of continuous, non-segregated L1₀ FePt thin films. These provide a model medium for heat-assisted magnetic recording and more generally for spintronic devices such as magnetoresistive random access memory and spin torque oscillators, where very high perpendicular magnetocrystalline anisotropy is required. Varying the target DC bias voltage, which in RPS can be tuned independently of the plasma generation, produces no meaningful, statistical change in average grain size, 6.5 ± 0.1 nm, for as-deposited, disordered FePt. Annealing at 800 °C creates the well-ordered L1₀ phase but results in an increased average grain size of 8.3–13.6 nm, and a significantly wider grain size distribution of 6.4–8.5 nm. These results show that whilst RPS is capable of producing well-ordered L1₀ FePt thin films, it does not offer an advantage in controlling the grain size of FePt, as reported in other thin film systems.