Study of Sintered Magnets of the Nd-Fe-B Type

Abstract : This is the final report of a 3 1/2-year effort to assess the utility and limitations of Nd-Fe-B based sintered magnets for microwave devices such as traveling wave tubes. In these devices, the magnetic properties at elevated temperatures are of importance, as is the flux stability during thermal cycling and long-term exposure. The experimental work described here involved several tasks: 1) the characterization of magnets from industrial RD 2) development of our own techniques and the capabilities for preparing Nd-Fe-B alloys and sintered magnets from them; 3) modification of the alloy compositions and heat treatments in order to improve the elevated temperature magnetic properties, making the magnets more suitable for applications in the 100 to 200 deg C range at low operating permeance values; and 4) the attempt to better understand the magnetization reversal behavior and the relationship between coercivity and microstructure. Keywords: Permanent magnets; Magnetic stability; Coercivity; Temperature compensation; Traveling wave tubes.