INTERLAYER COUPLING BETWEEN FE3O4 LAYERS SEPARATED BY AN INSULATING NONMAGNETIC MGO LAYER

The magnetic interlayer coupling between two magnetic layers separated by an insulator was investigated on Co0.2Fe2.8O4/Fe3O4/MgO/Fe3O4 samp les grown by means of molecular beam epitaxy on (001) MgAl2O4 substrat es. The samples were designed to observe interlayer coupling of either sign. Hysteresis loop measurements show that the Fe3O4 layers are fer romagnetically coupled in the thickness range 0-45 nm MgO. Below a MgO spacer thickness of 1.3 nm, the coupling strength increases drastical ly with decreasing MgO thickness and is ascribed to the existence of f erromagnetic bridges through the MgO spacer. The small ferromagnetic c oupling above 1.3 nm seems to arise from a magnetostatic coupling due to correlated interface irregularities.