Dynamic Atomic Reconstruction: HowFe3O4Thin Films Evade Polar Catastrophe for Epitaxy

Polar catastrophe at the interface of oxide materials with strongly correlated electrons has triggered a flurry of new research activities. The expectations are that the design of such advanced interfaces will become a powerful route to engineer devices with novel functionalities. Here, we investigate the initial stages of growth and the electronic structure of the spintronic Fe3O4/MgO(001) interface. Using soft x-ray absorption spectroscopy, we have discovered that the so-called A-sites are ompletely missing in the first Fe3O4 monolayer. This discovery allows us to develop an unexpected but elegant growth principle in which, during deposition, the Fe atoms are constantly on the move to solve the divergent electrostatic potential problem, thereby ensuring epitaxy and stoichiometry at the same time. This growth principle provides a new perspective for the design of interfaces.