Enhancement of Polar Kerr Effect by Forming Cu Nanoparticles on Ni Surface

Cu(x)/Ni(y)/glass bi-layer films, with x ranging from 10 to 310 A andy = 85 A, were made by the vapor evaporation method in a good vacuum. The surface morphology of each bi-layer was examined by an atomic force microscope (AFM). The results show that when x = 10 and 40 A, respectively, there are, in particular, a large number of Cu nanoparticles (or nano-islands) forming on top of the Ni surface.As a result, we observed considerable enhancement of either the polar Kerr rotation (θk) or the extraordinary Hall coefficient (Rs) at these two thicknesses (e.g. checking the figure below). As well known, the penetration depth (δp), of the polarized electrons, crossing the Cu/Ni interface from the Ni to the Cu layer, is of the order of the electron mean free path, i.e. δp =(3/8)[Cu≈90 A. in the Cu layer. Therefore.the strong enhancement of θK is due to the enhanced surface plasma resonance effect on the polarized Cu nanoparticles. Moreover. the formation of Cu nanoparticles roughens the bi-layer's surface greatly.That means the enhancement of Rs is due to the increase of the surface resistivity ρs.