Realization of high-quality Sr4Fe6O13 epitaxial film and its phase competition with SrFeO2.5

Abstract

Oxides with heterostructures or superlattices have been a hot topic for a long time owing to blowout phenomena and broad applications in spintronics, ferroelectric devices and superconductors. The Sr4Fe6O13-type superlattice, a weak ferromagnet with unique electron-ion hybrid conductivity, has recently received much attention. However, due to the lack of a high-quality single crystal for research, the origin of its ferromagnetism and conductivity still needs to be addressed. Epitaxial films are an excellent method for obtaining high-quality single crystals with definite orientations and substrate-induced strains. In this study, Sr4Fe6O13 films are grown using pulsed laser deposition (PLD). A systematic investigation of the growth conditions is carried out to synthesize pure and high-quality Sr4Fe6O13 epitaxial films. A phase diagram is drawn to illustrate the effects of the growth conditions on the phases of the films after a series of experiments were conducted under various growth conditions. Based on the density functional theory calculations’ results, which strongly agree with the phase diagrams acquired from experiments, the competition of the formation of Gibbs free energies between Sr4Fe6O13 and SrFeO2.5 is addressed. An oxygen-deficient environment inhibits the growth of Sr4Fe6O13 but favors SrFeO2.5. The as-grown high-quality Sr4Fe6O13 epitaxial film is fully strained, and scanning transmission electron microscopy confirms its microstructure. Our findings can shed light on the development of other films with similar layered superlattice structures and investigate their intrinsic properties.