Effect of Additional Elements on the Crystallization Process in Fe-Ta-C Thin Films

The crystallization mechanisms of Fe-Ta-C alloy films added Nb and Cr were studied in terms of changes in the crystal structure and magnetic properties. The Fe-Ta-C thin films as prepared by sputtering have an amorphous like X-ray diffraction profile. However, microcrystals of TaC of about 5 nm size were observed by TEM. Through DSC measurement, the crystallization temperature of the Fe alloy film was determined to be 753 K. However, the diffraction peak of α-Fe started to appear at 713 K, and the complete crystallization of the film occurred at 753 K. The sturation induction Bs of a Fe-Ta-C thin film before annealing was 0.76 T. The α-Fe grain size of the Fe-Ta-C thin film after annealing was 5 to 12 nm. The coercive force was 720 A/m befor annealing at 823 K for 1800 s. After annealing this film at 823 K for 3600 s, the coercive force was 32 A/m, but in the magnetic film, a component with higher coercive force was formed. To control the Fe grain size, Cr which dissolves into α-Fe was added. To control the grain size of TaC, Nb which reacts to the carbon was added. When Nb and Cr were added to Fe-Ta-C, no microcrystal such as TaC was observed under TEM in the as deposited film, indicating that the film is in an amorphous state. The DSC measurements of the Cr- and Nb-doped films showed that the crystallization temperature is 787 K, higher than that in Fe-Ta-C films. The complete crystallization of Cr- and Nb-doped Fe-Ta-C alloy thin films occurred at the same temperature. The magnetic properties also changed at 787 K. The Bs value of the as-deposited Fe-Ta-Cr-Nb-C film was 0.1 T. This is smaller than that of the Fe-Ta-C thin film. This is consistent with the TEM observation of the as-deposited film. The coercivity Hc was 16 A/m, which is smaller than 32 A/m of the Fe-Ta-C thin film. High coercive force component as was seen in the Fe-Ta-C was not formed in the Fe-Ta-Nb-Cr-C film. Controlling the crystallization by adding elements such as Cr and Nb, we significantly improved the soft magnetic properties of Fe-Ta-C films.