Samarium-Cobalt Phase Equilibria Revisited; Relevance to Permanent Magnets

In the binary system Sm–Co the region between Sm Co (79.2 at.% Co) and Co is discussed. SmCo is not stable at low temperatures; it is transformed in the anomalous eutectoid reaction SmCo → Sm Co +Sm Co , and the experimental evidence does not support other assumptions about this process. In this rea...

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Bibliographic Details
Published in:	International journal of materials research Vol. 89; no. 2; pp. 114 - 118
Main Authors:	Stadelmaier, Hans H., Reinsch, Bernd, Petzow, Günter
Format:	Journal Article
Language:	English
Published:	De Gruyter 16-12-2021
Online Access:	Get full text
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Summary:	In the binary system Sm–Co the region between Sm Co (79.2 at.% Co) and Co is discussed. SmCo is not stable at low temperatures; it is transformed in the anomalous eutectoid reaction SmCo → Sm Co +Sm Co , and the experimental evidence does not support other assumptions about this process. In this reaction, the crystallization of Sm Co is suppressed or greatly retarded, leaving the appearance of simple precipitation of Sm Co . This precipitation, in any form, destroys the high coercivity that is otherwise obtained in sintered magnets. The conditions for possible spinodal decomposition are described, and it is shown why it cannot be responsible for the coercivity mechanism in binary SmCo . The partial replacement of Co by Cu in SmCo also leads to the precipitation of Sm Co but now, contrary to the behavior in binary Sm–Co, it actually enhances coercivity.
ISSN:	1862-5282 2195-8556
DOI:	10.3139/ijmr-1998-0023