EFFECT OF AL, CR, OR RU ADDITION ON CORRO SION-RESISTANCE OF FE-TA-C MAGNETIC THIN-FILMS

Effect of additional elements such as Al or Cr, Ru on the corrosion re sistance of Fe-Ta-C magnetic thin films was studied. The electrochemic al 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 passiv e 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 r ather low corrosion resistance. The AI doped Fe-Ta-C magnetic thin fil m (Al concentration is about 10 at%) is covered with a passive film, w hich has a high corrosion resistance. To study the difference of corro sion resistance among the films with different additional elements suc h as Al, Cr, or Ru the following model samples were prepared. In the m odel samples, as Al layer or a Cr layer was formed on the Fe layer. Th e depth profiles were studied by AES method after annealing these samp les. In the Al/Fe sample, Al diffuses into the Fe layer after annealin g 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 t he Fe/Cr interface. This result implies that the carbon at the Fe/Cr i nterface 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 sol id solution at the Cr/Fe interface. The bonding energies in these samp les were measured by the ESCA method. The bonding state of Cr in the F e-Ta-Cr-Ru-C film is metallic, and there exists another state of Cr wh ich could not be identified as a result of a broad peak width. Some of the Al atoms in the A-doped Fe-Ta-C film are in the metallic bonding state and some others are in the oxide state. Al is the most easily ox idized element among these elements. Thus, Al doped Fe-Ta-C alloy film has a high corrosion resistance. We have demonstrated that the effect ive 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.