Magnetizability of Nd-Fe-B-type magnets with Dy additions

Many alloying additions have been made into Nd‐Fe‐B‐type magnets to alter their permanent magnet properties, in particular for applications above 100 °C. To this end, a common practice has been to add Dy, increasing Hci [M. Sagawa, S. Fujimura, H. Yamamoto, H. Matsuura, and K. Hiraga, IEEE Trans. Magn. 20, 1584 (1984); M. Tokunaga, M. Meguro, M. Endoh, S. Tanigawa, and H. Harada, ibid. 20, 1964 (1985)]. It is not unusual to find Hci >20 kOe in these substituted alloys. This approach has caused a dilemma. In some cases, increasing Hci above 20 kOe makes the alloy more difficult to magnetize and therefore less useful when the field available for magnetizing is 25 kOe or less. We have examined the effect of various alloying additions and heat treatment on the magnetizability of substituted Nd‐Fe‐B alloys. We show that high Hci at room temperature is not a necessary requirement to have Hci >6 kOe at 150 °C. We discuss the factors affecting the magnetizability of Nd‐Fe‐B‐type magnets.