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Interfaces often exhibit unique electronic and magnetic properties that are not present in their bulk constituents. Understanding the atomic-level structure and properties of the interface is crucial for their technological applications. In this article, we report a first-principles study of the γ-FeSi2/Si(001) interface to unravel the atomic-level structure property relationship. An external electric field is included in our model to tune the properties of the interface. Based on our calculations, we found a modest application of an electric field (> 0.15 eV/Å) could stabilize a sixfold and sevenfold coordinated, spin-active interface over a nonmagnetic (eightfold coordinated) interface-providing direct evidence of electric field control of magnetism at the interface. The sixfold as well as sevenfold coordinated structures are shown to favor antiferromagnetic spin ordering arising from the Fe(d)-Si(p)-Fe(d) super-exchange interaction. The distinct non-linear response of the interface structure to the applied electric field can be attributed to the different electronic and magnetic structures at the interface; the sixfold exhibits the highest polarizability over the other coordinated structures. [ABSTRACT FROM AUTHOR]