The structure, anisotropy and coercivity of rapidly quenched TbCu7-type SmCo7−xZrx alloys and the effects of post-treatments

The effects of wheel speed, Zr content, post-ball milling process and heat treatment on the structure, anisotropy, magnetic properties and phase transition of the melt-spun SmCo7−xZrx alloys were investigated. The crystallographic c-axis is parallel to the ribbon plane for the ribbons prepared at low speeds of 5 and 15 m/s, and this orientation is reduced at higher speeds. The out-of-plane coercivity of SmCo6.8Zr0.2 ribbon increases from 123 kA/m for 5 m/s to 1076 kA/m for 60 m/s. Zr doping improves the hard magnetic properties and the in-plane coercivity of SmCo7−xZrx alloys increases with the Zr content from 592 kA/m for x=0.1 to 1376 kA/m for x=0.4. The Rietveld refinements and theoretical analysis reveal that Zr atoms occupy the 2e site. The coercivity mechanisms are different for the alloys with various Zr contents. The ball milling process could enhance the coercivity and remanence of the ribbons due to the grain refinement and the precipitation of Co phase. Heat treatment can further modify the magnetic properties of the alloys. SmCo6.7Zr0.3 alloy heat treated at 400 °C has the high maximum energy product (BH)max of 64.5 kJ/m3, where the coercivity was enhanced to 1560 kA/m by 650 °C heat treatment. In addition, the SmCo7−xZrx alloys exhibit excellent hard magnetic properties at elevated temperatures.