Phase equilibria and magnetic characteristics of phases in the MM-Co-Fe system at the high transition metal side

Abstract

The phase equilibria in the Mischmetal (MM)-Co-Fe system has been studied at 900°C as a ternary system with Indian MM containing 6 percent Fe. The ternary system shows considerable extensions of the binary 2:17,1:5 and 2:7 phases; as Fe content increased the extensions of the narrow phase regions deviated from the ideal stoichiometry line toward higher transition metal side. Existence of the 5:19 phase was detected in the RE-Co binary. In addition three new ternary phases, the S, T and A phases, were detected at higher Fe contents. The S and T phases extended along the 2:17 stoichiometry line whereas the A phase extended along the same line as the 2:17 phase. Curie temperature (Tc) and easy axis of magnetisation of the phases were determined. The Tc of S and 2:17 phases decreased from > 800°C with increasing Fe. While Tc for the A and T phases also decreased, it remained more or less the same for the 1:5 and 2:7 phases as Fe content was increased. Using magnetically aligned needles in a Weissenberg camera the easy axis of magnetisation of the S and 1:5 phases showed along the [0001] direction. The results thus show that the previously reported change of easy axis for the MM2Co17 phase with increase in Fe content is actually due to the presence of a new phase, the S phase.