Soft magnetic properties and film structures of Fe-C/Ta multilayered films

Fe-C/Ta multilayered films with low Ta diffusion into Fe are examined to find thermally stable soft magnetic Fe-based multilayers. Although coercivities of Fe-C/Ta multilayered films increase after heat treatment at 300–400 °C, they decrease to <200 A/m after heat treatment at 500–600 °C. Relative permeabilities of the multilayers with C concentrations of 5–7 at. % are 3000 at 500–600 °C, corresponding to the low coercivities. The magnetostriction constant changes from positive to negative as the heat-treatment temperature increases. Fe-C/Ta multilayered films show clear periodic structures at 300–600 °C. However, the periodic structure disappears and Fe crystallite growth occurs at 700 °C.