Elevated temperature behavior of sintered Nd-Fe-B type magnets

The effects of elevated temperature air exposure at 75 degrees , 100 degrees , 125 degrees , and 150 degrees C on the performance of sintered Nd-Fe-B type permanent magnets was investigated. The observations include a comparison of the initial and final demagnetization curves after long-term aging in excess of 5000 h, initial irreversible losses on heating, and the stability of open-circuit remanent flux as a function of time, temperature, and operating-point permeance. Test samples were obtained from four magnet producers. The results reported may be typical for present commercial production magnets made from ternary Nd-Fe-B and from alloys modified with dysprosium and cobalt. Test results indicate that there are very restrictive operational limits imposed by a combination of elevated temperatures >or=125 degrees C, and unit permeance values>