Variation of the Magnetic Properties of Sm (Co, Cu)<SUB>5</SUB> Alloys with Temperature

Abstract

Modified permanent magnets of rare earth cobalt compounds, R(Co, Cu)5, are known as alloys having a complex decomposition mechanism. Studies of the variation of magnetic properties with temperature were carried out for Sm(Co, Cu)5 alloys containing 0 to 75 at% copper. The optimum area for magnetic values was shifted toward the samarium-poor side from the line connecting the compound SmCo5 with SmCu5. Differential thermal analysis (DTA) revealed that the endothermic reaction temperatures were around 920°C and scarcely varied in alloys containing from 16 to 66 at% copper. This suggests that the phase transformation may occur at this temperature regardless of different copper contents. In Sm(Co, Cu)5 alloys a single Curie point (Tc) was observed on rapid heating from the as-cast condition, and two points on slow cooling after heating at 1000°C for 30 min. One of the Curie points belongs to a SmCo5 structure type and the other to a compound isostructural with Sm2Co17. From the results of DTA and measurements of Tc and magnetic values, a hypothetical Sm–Co–Cu ternary phase diagram is proposed, in which the alloys initially containing 24 to 40 at% copper may decompose spinodally.