HYSTERESIS CHARACTERISTICS OF CAST PERMANENT-MAGNETS MADE OF PR-FE-CO-B-CU ALLOYS

The influence of Co substitution for Fe on magnetic hysteresis propert ies of cast permanent magnets of the Pr-(Fe, Co)-B-Cu system has been studied. It was shown that an increase in the Co concentration up to 2 5 at.% is accompanied by an approximately linear growth of the Curie t emperature T-c of the base phase Pr-2(Fe, Co)(14)B, but the coercive f orce H-c of magnets is lowered to 1.5 kO. The drop in H-c is associate d with the occurrence of additional magnetically soft phases Pr-2(Fe, Co)(17) and Pr(Fe, Co)(2), as well as with the increase in the grain s ize of the base phase. Addition of aluminium and gallium inhibits a gr ain growth and raises H-c. The optimum conditions of homogenization an d annealing of the alloys Pr20Fe48.1Co25B5CU1.5(Al, Ga)(0.4), make it possible to obtain cast permanent magnets with T-c = 520 degrees C, B- r = 5.5 kG, H-c = 5 kO, and the temperature coefficient of induction 0 .05%/deg.