Interplay of structure and magnetism in surfactant-assisted grown metastable Fex Cu1-x alloy films

NIÑO, M.A; CAMARERO, J.; MIKUSZEIT, N.; DE MIGUEL, J.J.; MIRANDA, R.; GÓMEZ, L; FERRÓN, J; ABRUJAN, R.; FUKUMOTO, K; KUCH, W; WANG, S. G; TIEG, C; KIRSCHNER, J

Francia

Conferencia; J.. ECOSS 24, 24th European Conference on Surface Science; 2006

Artificial Fe­Cu alloy films are prepared in­situ at room temperature on a Cu(111) substrate by thermal coevaporation, using a Pb layer as surfactant to reduce the film roughness and the atomic mobility, thus preventing the segregation of the two components. These random alloy films retain the fcc structure for several nanometers of thickness, depending on the Fe concentration up to a maximum of 70%. The fcc­to­ bcc transition can be controlled using Fe concentration and temperature as parameters. The growth process has been analysed with the help of Monte Carlo simulations in continuous space, describing the atomic interactions by means of realistic empirical potentials. These simulations confirm the experimentally observed preservation of the fcc structure during the early stages of growth, and the gradual appearance of dislocations and lattice distortions eventually leading to an fcc­to­bcc transformation. The magnetic characteristics of these metastable alloy films have been studied by means of Magneto­Optic Kerr Effect and X­ray Magnetic Circular Dichroism measurements. These experiments reveal the presence of a buried layer of paramagnetic alloy that remains fcc at room temperature even after the upper layers have turned ferromagnetic and bcc. At low temperature, though, a reversible para­ to ferro­magnetic transition has been observed in this layer, correlated with structural transformations. Finally, a relatively strong (0.1 µ B) induced magnetic moment is found at the Cu atoms, aligned parallel to that of the Fe.