Magnetic properties and microstructure of melt-spun Sm(Co,Fe,Cu,Zr)8 magnets

We report on the microstructural and magnetic properties of rapidly quenched Sm(Co_balFe_0.1Cu_xZr_0.04)₈ ribbons. Samples spun at velocities above 40 m/s are nanocrystalline and magnetically hard, even in the as-spun state. The coercivity and its temperature coefficient can be improved by annealing at 750°C. Samples spun at low speeds have low coercivity in the as-spun state and are characterized by larger grain sizes. By annealing a cellular precipitation structure within the grains, similar to that of bulk Sm(Co,Fe,Cu,Zr)_z magnets, can be obtained in Cu-containing samples, resulting in an increase of the coercivity, since the precipitates act as pinning centers. Some precipitation occurs even in as-spun Cu-free samples, indicating that their formation is not directly related to the existence of Cu, in contrast to the cellular structure. Compared to the bulk materials, lower annealing temperatures and shorter heat treatment times are required and the slow cooling process is not needed. The activation volumes for the magnetic reversal process are estimated by magnetic relaxation measurements.