Structure and magnetic properties of magnetron-sputtered Fe/Cu multilayered thin films

The structure and magnetic properties of Fe/Cu multilayered films with a constant total Fe thickness of 1050 Å but varying Fe-layer thickness from 6.3 to 42 Å and varying Cu to Fe thickness ratio from 1 to 3 were investigated using x-ray diffraction (XRD), x-ray absorption fine-structure (XAFS) spectroscopy, and magnetic measurements. Samples were prepared at room temperature on mica, glass, and silicon substrates using the dc-magnetron-sputtering method. For films with the same Fe-layer thickness, it was found that the magnetic moment of Fe decreases with increasing thickness ratio of Cu to Fe. For films with a Cu to Fe thickness ratio of 3, it was found that the magnetic moment of Fe decreases with decreasing thickness of the individual Fe layers. XRD and XAFS results revealed that in the multilayered films, Cu has a well-defined fcc structure with minimal amount of structural disorder independent of the individual layer thickness or thickness ratio. On the other hand, quantitative analysis of EXAFS data revealed that the crystal structure of Fe changes with decreasing thickness of the Fe layers from distorted bcc (for 42- and 21-Å-thick Fe layers) to fcc (for 10.5- and 6.3-Å-thick Fe layers) in films with the Cu layer three times thicker than the Fe layer. The single-phase fcc Fe of the 6.3-Å Fe/19-Å Cu multilayered film was found to have a lattice constant of 3.596 Å and is ferromagnetic with a Curie temperature of 210 K and a spontaneous magnetization of ∼690 emu/${\mathrm{cm}}^3$.