Magnetic interaction in small iron-copper clusters

Abstract

In this work we report a Mössbauer study of iron-copper clusters isolated in a rare gas solid. For the FeCu dimer we were able to determine the electronic ground state. The samples were prepared in a liquid-helium cryostat evacuated to a pressure better than 10−7 torr. The Cu and (90% enriched) 57Fe atomic beams were produced in alumina crucibles contained in resistance heated tantalum furnaces and codeposited with a stream of argon gas at 4.2K onto a Be disk. In this study very dilute samples were used (Ar/metal ?500) in order to identify correctly the FeCu dimer. From the Mössbauer parameters we were able to identify the molecule as 2π with a spin at the iron atom of 1/2. A concentration dependence study of the iron-copper multimer was carried out. It was observed that by increasing the number of copper nearest neighbors the isomer shift approaches the value obtained for iron in a copper matrix. For very high concentrations the Mössbauer parameters are similar to those of pure iron multimer. It seems that the presence of a large number of copper nearest neighbors produces a drastic change in the electronic structure of the iron atom.