The Structure of Co-Cu-Ce Permanent Magnet Alloys

Following the discovery by Nesbitt et al that Cu additions to Co 5 Ce produced an age hardenable permanent magnet of exceptional quality, considerable effort has been devoted to understanding the effect of metallurgical processing on these alloys. Aside from work on the Co-Cu-Sm system, direct observation of the alloy structure responsible for the high coercivity of these alloys has not been reported. Our purpose here is to present a preliminary account of such observations. The alloy employed in this study was directionally solidified Co 3 .8Fe O .5Cu O .9Ce. The boule was spark cut perpendicular to the growth axis into 1 mm thick wafers, sealed under vacuum in quartz ampoules, and heat treated. The wafers were prethinned by electropolishing and profiled by jet polishing in H 3 PO 4 saturated with Cr 2 O 3 at 100°C. During jet polishing the samples were sandwiched between gold grids. Final thinning was accomplished by ion milling.