The interface of Mn, Fe, Co and Au metal films on NiO(0 0 1), investigated by photoemission and low energy electron diffraction

Ferromagnetic (FM) and antiferromagnetic (AFM) multilayers are promising candidates for new magnetic sensors with spin-valve properties. At room temperature, thin films with a thickness of about 1.5 nm, of Mn, Fe, Co and Au were deposited on single crystalline NiO(0 0 1), grown epitaxially on bulk Ag(0 0 1). Also, an Au film was deposited on pure Fe, in order to investigate chemical protection properties. The FM/AFM interface plays a decisive role with regard to the magnetoresistive properties of layered magnetic structures. Photoemission and low energy electron diffraction provide an access to a better understanding of the chemical and structural processes within the metal/NiO interface. In addition to a change of the metal film structure by annealing, the main finding is, that the deposited reasonable epitaxially metal films induce a remarkable chemical reduction of nickel oxide to nickel metal at the metal/NiO interface. This result implies, that the interface is not a sharp, well-defined, quasi two dimensional plane, but rather a region extending over several monolayers, consisting of a complex chemical and structural composition originating from the chemical reaction with the oxygen as well as atomic diffusion processes. These findings show, that it seems nearly impossible to produce sharp metal/NiO interfaces, which are thought to be necessary to significantly improve magnetoresistive properties. The Au film on pure Fe did not show the desired protection properties against oxidation of the substrate, when the sample was brought to ambient atmosphere for a few minutes.