Transverse electrical resistivities have been measured on Fe 3 O 4 /NiO modulated structures of varying modulation wavelength L. A dependence of the resistivity on L is observed in which the resistivity rapidly increases many orders of magnitude as the modulation wavelength decreases from the bulk L !`limit in the vicinity of 600 Å. A qualitative argument is presented for a metal-insulator-metal interfacial-charge-transfer model which contains both the resistivity enhancement and the observed length scale dependence. [S0031-9007(96)