Effect of Pre-Aging Treatment on the Microstructure and Magnetic Properties of Sm(Co,Fe,Cu,Zr)<sub>7.8</sub> Sintered Magnets

The effects of pre-aging treatment on the microstructure and magnetic properties of Sm(Cobal.Fe0.35Cu0.06Zr0.02)7.8 were investigated. The main phase of both solution-treated magnet and pre-aged magnet was the 1 : 7 phase, and there were no distinct differences between the X-ray diffraction profiles of these magnets. Fine Cu-rich precipitates a few tens of nanometers in size were observed in pre-aged magnet by scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy mapping, but such precipitates were not observed in solution-treated magnet. As for fully aged magnets, the cell size was smaller in pre-aged magnet than in non-pre-aged magnet. Thus, the pre-aging treatment gave a fine cellular structure. Mr and HcJ of pre-aged magnet were almost same as those of non-pre-aged magnet. Squareness of the demagnetization curve for fully aged magnet was increased by pre-aging treatment. As a result, (BH)max of magnet subjected to pre-aging treatment was greater than that of magnet not subjected to pre-aging treatment. The fine cellular structure seemed to result in higher squareness. The following magnetic properties were obtained for Sm(Cobal.Fe0.35Cu0.06Zr0.02)7.8 by pre-aging treatment: Mr = 1.24 T, HcJ = 1490 kA/m, and (BH)max = 266 kJ/m3.