Controlled grain growth in granular FePt–SiO2 thin films under single pulsed laser anneals

The high magnetocrystalline phase of L10 FePt has received considerable attention for achieving stable magnetization states in small volumes which could increase magnetic areal storage densities. When FePt is sputter-deposited, it adopts a magnetically soft A1 phase requiring annealing to phase transform to the L10 phase; this annealing results in detrimental grain growth which reduces the capacity for high areal storage densities. In the current work, a series of 10 nm thick granular FePt–SiO2 thin films with various silica contents has been annealed at different fluences using a 10 ms pulse width, 1064 nm wavelength laser to determine if the silica matrix could inhibit this grain growth. The A1 to L10 phase transformation was confirmed by selected area electron diffraction. In general, the films annealed with approximately 25 J/cm2 exhibited the highest L10 c/a tetragonality, 0.97, and coercivity of approximately 875 kA/m (11 kOe). For these films, the 38 vol.% silica incorporation resulted in a FePt grain size of approximately 8.5 nm as compared to 30 nm for films with no silica. The granular encasement of the FePt grains was effective at reducing but unable at inhibiting grain growth using single pulsed laser anneals.

► Grain growth was hindered by laser annealing in a granular matrix.
► Laser annealing allowed the preservation of the granular microstructure.
► Fluences exceeding 25 J/cm2 resulted in microstructure breakdown.