1996 Volume 60 Issue 12 Pages 1251-1258
Effect of additional elements such as Al or Cr, Ru on the corrosion resistance of Fe-Ta-C magnetic thin films was studied. The electrochemical characteristics of Al, Cr, or Ru doped Fe-Ta-C magnetic thin films were measured. For the Fe-Ta-C thin film doped with Cr or Ru, a passive layer is formed on the surface of the film. However, the protection current of the passive layer is so high that the magnetic film has a rather low corrosion resistance. The Al doped Fe-Ta-C magnetic thin film (Al concentration is about 10 at%) is covered with a passive film, which has a high corrosion resistance. To study the difference of corrosion resistance among the films with different additional elements such as Al, Cr, or Ru the following model samples were prepared. In the model samples, as Al layer or a Cr layer was formed on the Fe layer. The depth profiles were studied by AES method after annealing these samples. In the Al/Fe sample, Al diffuses into the Fe layer after annealing at 773 K. But, on the Cr/Fe sample, Cr does not diffuse into the Fe layer by annealing at 973 K, it was also found that carbon exists at the Fe/Cr interface. This result implies that the carbon at the Fe/Cr interface supresses the diffuse of Cr into the Fe layer. As a results, a solid solution is formed at the Fe/Al interface, but there is no solid solution at the Cr/Fe interface. The bonding energies in these samples were measured by the ESCA method.
The bonding state of Cr in the Fe-Ta-Cr-Ru-C film is metallic, and there exists another state of Cr which could not be identified as a result of a broad peak width. Some of the Al atoms in the Al-doped Fe-Ta-C film are in the metallic bonding state and some others are in the oxide state. Al is the most easily oxidized element among these elements. Thus, Al doped Fe-Ta-C alloy film has a high corrosion resistance. We have demonstrated that the effective additional elements for improving the corrosion resistance of the magnetic film are those which have a high diffusivity into Fe, without forming carbides, and which form a passive film on the surface of the magnetic thin film easily.
