Microstructurcal and magnetic investigations into the origins of high coercivity 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 optical and electron microscopy, differential thermal analysis, and superconducting quantum interference device magnetometry that was performed 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 relatively superior remanence, 7.7 kG, but poor coercivity, 2.7 kOe, while 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 same character and morphology for all three samples and shows no evidence of intragranular carbon, which is demonstrated to reside in the impurity phases. The superior coercivity found in Pr18Co76C6 is attributed to a previously unknown triclinic phase, Pr3Co4Cx (x approximate to 3-4) that appears to undergo a magnetic-nonmagnetic transition with increasing temperature around T = 80 K. The variety of magnetic properties exhibited by each sample is due to the variety of minor phases present in each sample, which may be a product of the effect that carbon has on the solidification rate of the parent alloy. (C) 1996 American Institute of Physics.