TEM studies of cobalt-rare earth permanent magnets

Abstract

The microstructures of several cobalt-rare earth magnet alloys from various laboratories were examined by transmission electron microscopy (TEM). The magnets varied in alloying elements and in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</tex> , the ratio of transition-metal to rare-earth atoms. Matsushita magnets with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z\sim8</tex> had a relatively featureless microstructure. Toshiba magnets with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z\sim7</tex> contained a fine cellular microstructure, and Brown-Boveri magnets with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z=7.8</tex> contained fine isolated precipitates plus a partly-formed cellular structure. These observations are consistent with magnetization hehavior, which indicated nucleation-controlled coercivity for the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z\sim8</tex> magnets and pinning-controlled coercivity for the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z\sim7</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z=7.8</tex> magnets. Results are compared with earlier TEM studies.