Further Magnetic and Thermal Studies of Cast Rare-Earth Permanent Magnets

Abstract

Studies have been made of the effect of composition on the magnetic properties of arc‐cast alloys in the vicinity of Co_3.5CuFe_0.5Ce. The residual induction varies from 4000 to 6400 G with intrinsic coercive force values from approximately 5000 to 12 000 Oe. The maximum energy product values range from about 4 to 10×10⁶ G Oe, the higher values generally associated with alloys of lower copper content. Freezing points of these alloys were determined for the first time using differential thermal analysis. Solidification occurs over a range of temperatures; initial freezing point decreases from 1177°C for a low copper alloy (Co_3.94Cu_0.5Fe_0.56Ce) to 1124°C for a high copper alloy (Co_2.63Cu_2.0Fe_0.36Ce). Several additional peaks were observed in the cooling curves after the initial freezing had occurred. These peaks are tentatively attributed to additional phases which are likely in view of the complexity of the Co–Ce and Cu–Ce binaries. The precipitation reaction at 400°C which was previously observed by metallography was evidently too weak to be detected in the DTA analysis. Measurement of magnetization versus temperature indicated that Curie temperatures are generally above 700°C depending on composition and heat treatment.