Effect of zirconium upon structure and magnetic properties of 2-17 type rare earth-cobalt magnets

Crystalline ribbon specimens with compositions of Sm(Co0.70-xFe0.20Cu0.10Zrx)7.5(x=0-0.06) are prepared in argon atmosphere by a melt-spinning technique to examine the phase constitution, microstructure and magnetic properties and to determine the effect of Zr addition in the magnet alloys. In an as-prepared state, they predominantly consist of a single 1-7 phase, except for a specimen with x=0, which includes a small amount of 1-5 phase. After the optimum aging, the coercivity increases markedly with increasing Zr content, to reach the maximum value of 14.5 kOe at x=0.04. During the aging, the 1-7 phase transforms into a cellular structure composed of 2-17 and 1-5 phases to attain the high coercivity due to the domain wall pinning mechanism. In the specimen with higher Zr content, another kind of phase is precipitated in a platelet form, to overlap the cellular structure. This phase is identified as a 1-3 phase of (Sm,Zr)(Co,Fe,Cu)3and presumably contributes to the coercivity enhancement.