MICROSTRUCTURCAL AND MAGNETIC INVESTIGATIONS INTO THE ORIGINS OF HIGHCOERCIVITY IN DIE-UPSET PRASEODYMIUM-COBALT-CARBON BASED MAGNETS

Melt-quenched and thermomechanically deformed samples with the nominal compositions Pr18Co82, Pr18Co81C, and Pr18Co76C6 were examined with o ptical and electron microscopy, differential thermal analysis, and sup erconducting quantum interference device magnetometry that was perform ed in the temperature range 20 K less than or equal to T less than or equal to 300 K. At room temperature, Pr18Co82 exhibits poor coercivity and remanence, 600 Oe and 2.9 kG, respectively. Pr18Co81C exhibits re latively superior remanence, 7.7 kG, but poor coercivity, 2.7 kOe, whi le Pr18Co76C6 exhibits the opposite trend, B-R = 4.5 kG and H-ci = 12 kOe. The main phase present in all samples, PrCo5, has basically the s ame character and morphology for all three samples and shows no eviden ce of intragranular carbon, which is demonstrated to reside in the imp urity phases. The superior coercivity found in Pr18Co76C6 is attribute d to a previously unknown triclinic phase, Pr3Co4Cx (x approximate to 3-4) that appears to undergo a magnetic-nonmagnetic transition with in creasing temperature around T = 80 K. The variety of magnetic properti es exhibited by each sample is due to the variety of minor phases pres ent in each sample, which may be a product of the effect that carbon h as on the solidification rate of the parent alloy. (C) 1996 American I nstitute of Physics.