Influence of cerium content on the structure and magnetic behavior of Co-Fe-Cu-Ce permanent magnets

As part of a continuing program to understand and optimize the magnetic behavior of Co-Fe-Cu-Ce permanent magnet alloys, we have made studies on the alloy system Co3.5Fe0.5CuCexwith x in the range 0.8 to 1.2. An alloy of x = 1 had previously been studied in detail and found to have good permanent magnet properties. In the present work, it was found that when x > 1, the coercive force was increased while both the Curie temperature and saturation magnetization were decreased. However when x < 1, the coercive force tends to decrease while the Curie temperature and saturation magnetization increase. The increase in coercive force with increase in cerium content can be accounted for largely by the decrease in saturation magnetization. These results are in accord with a domain wall pinning mechanism. Scanning electron microscopy studies have shown that a major second phase in the low cerium alloys is low in copper as compared with the matrix. On the contrary, the copper content of the second phase in the high cerium alloys is larger than that in the matrix.