Harnessing two-step heating and solid-state dewetting for highly ordered L10-FePd alloy epitaxial films

L 1 0 -ordered FePd epitaxial films with a nominal thickness of 5 nm were grown by r.f. magnetron sputtering on the SrTiO 3 (001) single crystal substrates by a two-step heating method. A subtle 50 K change in the first-heating temperature of a two-step process drastically alters the morphological trajectory of L 1 0 -FePd films, switching among three regimes: (i) Frank–van der Merwe (FM — atomically flat ), (ii) Solid-state dewetting (SSD — square holes ), and (iii) Stranski-Krastanov or late-stage SSD (SK or SSD late stage — 3D grains ). (i) [FM mode] Almost no lattice disturbance in the in-plane direction, and perfect constraint by tensile strain from the SrTiO 3 substrate was achieved. (ii) [ SSD mode ] Square holes penetrating to the SrTiO 3 substrate were formed, and sides of the square were grown along the or of the SrTiO 3 substrate. According to first-principles calculations, a large difference in surface free energy between L 1 0 -FePd and the SrTiO 3 substrate is predicted. This difference in surface free energy is the minimum necessary condition for SSD to occur. The trigger for SSD is small holes/voids formed during the 1 st heating process in the two-step heating process. (iii) [SK or late-stage SSD mode] Grains grew 3-dimensionally, which can be considered as SK growth mode or the late stages of SSD. Note that the 1 st heating temperature of the two-step heating process significantly changed the morphological trajectory, even though the 2 nd heating temperature of 600°C was significantly higher than that of the 1 st growth temperature. The SSD reduced the substrate restraint, resulting in the highest degree of L 1 0 -ordering (S L10 = 0.99) and the highest perpendicular magnetic anisotropy (PMA = 1.33MJ/m 3 ).