Magnetic Properties of Ultrathin Magnetite Films Grown by Molecular Beam Epitaxy

Magnetic properties as a function of film thickness (2-55 nm) for magnetite (Fe₃O₄) thin films grown on MgO (100) substrates show that the small thickness films (les 5 nm) are ferromagnetic and possess magnetization values which are much greater than that of bulk Fe₃O₄ . 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 Fe₃O₄-MgO interface and it turns out that the noncompensation of spin moments between the two magnetic sublattices of spinel Fe₃O₄ is a major factor contributing to the enhancement of magnetization.