Observation of interfacial electrical polarization inFe3O4/NiO superlattices

The dielectric permittivity of ${\mathrm{Fe}}_3$ ${\mathrm{O}}_4$/NiO superlattices reveals frequency-dependent features, not found in the constituent materials, which we identify as due to interfacial (Maxwell-Wagner) electrical polarization. Large modulations of the displacement field within 34 Å of an interface have thus been observed. We find further evidence that the low-frequency dielectric constant is half the value and the interfacial relaxation time is ∼10 times larger in a 34 Å/34 Å superlattice than expected suggesting that the short superlattice wavelength is less than the length scale required to define ‘‘bulk’’ polarization and conductivity.