Magnetic Properties of Ultrathin Magnetite Films Grown by Molecular Beam Epitaxy

Magnetic properties as a function of film thickness (2–55 nm) for magnetite (Fe $_{3}$O$_{4}$) thin films grown on MgO (100) substrates show that the small thickness films ($\leq 5$ nm) are ferromagnetic and possess magnetization values which are much greater than that of bulk Fe$_{3}$O$_{4}$ . The inverse thickness dependence of the magnetization points to an interface related mechanism. Whereas, our detailed spin polarized density functional theoretical calculations suggests that there is only a marginal enhancement in the local spin moments of Fe-atom in the vicinity of the Fe$_{3}$O$_{4}$-MgO interface and it turns out that the noncompensation of spin moments between the two magnetic sublattices of spinel Fe$_{3}$O$_{4}$ is a major factor contributing to the enhancement of magnetization.