Theoretical Insight into the Origin of Dielectric and Magnetoelectric FeCo Alloy–Metal Fluoride Insulators

FeCo alloy–metal fluoride nanogranular films are known for their significant magnetoelectric responses, which are useful as several electromagnetic devices. In this study, we analyzed the interfaces between (110) FeCo and various clusters of metal fluorides (MgF2, AlF3, and YF3) to understand the origin of the large dielectric and magnetoelectric response caused by metal fluoride insulators through density functional molecular dynamics (DF-MD). Our DF-MD computations revealed that the metal fluoride clusters adhered to the (110) FeCo surface via Co/Fe–F bonds. The electronic structures of the (110) FeCo surfaces with the adsorbed metal fluoride clusters showed that FeCo was oxidized by the metal fluorides, resulting in polarization at the interface. Additionally because metal fluorides contain extra electrons, they can be magnetic, and the performance of electromagnetic devices depends on the electron affinity of fluoride insulators and the orbital magnetic moment of their acceptor levels.