No abstract

Au ( x ) ∕ Ni ( y ) ∕ glass ( sub ) bilayered films, with x ranging from 0to310Å and y=85Å, were made by the vapor evaporation method in vacuum. The surface morphology of each bilayer was examined by an atomic force microscope. The results show that when x=xm=25 and 100Å, respectively, there were, in particular, a large number of Au nanoparticles (or nanoislands) forming on top of the Ni surface. As a result, we observed considerable enhancement in either the polar Kerr rotation θK or the extraordinary Hall coefficient RS at these two thicknesses. As is well known, the penetration depth δP of the electron transverse flow, crossing the Au∕Ni interface from the Ni to the Au layer, is of the order of the electron mean free path ℓAu, i.e., δP=(3∕8)ℓAu≈116Å, in the Au layer. Hence, the situation xm<δP is always satisfied. Then, the strong enhancement of θK is due to the surface plasma resonance effect on the Au nanoparticles (e.g., by reducing the real part of the diagonal dielectric tensor εxx so that Re[εxx(ω)]≈1, where ℏω=1.96eV). Moreover, the formation of Au nanoparticles roughens the bilayer’s surface. That means the enhancement of RS is due to the increase of the surface resistivity ρS. Finally, since the side-jump mechanism is effective, it could affect θK too (e.g., by enhancing the imaginary part of the off-diagonal conductivity Im[σxy]).