The microstructure, strain state and optical properties of FePt nano-clusters in MgO matrix

Highlights: • MgO matrix could effectively suppress the coalescence of FePt clusters. • The shape of FePt clusters lies on its strain state. • The absorption peaks is attributed to the existence of grain boundary and defects. The FePt nano-clusters (NCs): MgO nanocomposite films were successfully fabricated by pulsed laser deposition at 650 °C. In-situ reflection high-energy electron diffraction (RHEED) analysis indicates the existence of epitaxial strain in the FePt cluster. This strain was identified quantitatively (1.2% and 0.66% at in-plane and out-of-plane direction) via strain mapping by geometric phase analysis (GPA) at nano-scale. A further microstructure investigation by transmission electron microscopy (TEM) shows the lop-angle triangle structure of FePt NCs, which is considered to be caused by the strain difference in two directions. Two absorption peaks has been observed in the range of 4–6.5 eV by ultraviolet–visible, which were attributed to the existence of grain boundary and defects caused by the embedding of FePt in MgO. This work provided important information for its further research and performance improvement in many potential applications.