Magnetic properties, domain structure, and microstructure of anisotropic SmCo 6.5 Zr 0.5 ribbons with C addition
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Magnetic properties, domain structure, and microstructure of anisotropic SmCo6.5Zr0.5 ribbons with C addition A-Ru Yan, Zhi-Gang Sun, Wen-Yong Zhang, Hong-Wei Zhang, and Bao-Gen Shen State Key Laboratory of Magnetism, Institute of Physics and Center of Condensed Matter Physics, Chinese Academy of Science, Beijing 100080, People’s Republic of China (Received 15 March 2000; accepted 28 December 2000)
The magnetic properties and the domain structure of anisotropic melt-spun SmCo6.5Zr0.5 alloys with C addition was investigated by means of x-ray diffraction (XRD), magnetic measurement, and magnetic force microscopy. The XRD analyses showed that the addition of a few percent of C led to a significant increase in the coercivity and simultaneously affected the characterization of crystalline texture of the ribbons. The easy magnetization c axis changed from parallel to the ribbon plane for SmCo6.5Zr0.5 ribbons to normal to the ribbon plane for SmCo6.5Zr0.5C0.25–0.75 ribbons. An optimal coercivity of 0.92 T was obtained for the SmCo6.5Zr0.5C0.5 ribbon spun at 5 m/s. The corresponding remanence measured normal or parallel to the ribbon plane was 7.1 kGs or 3.1 kGs, respectively. The domain structure was studied by magnetic force microscopey. A strip-shaped domain was observed on the surface of the SmCo6.5Zr0.5 ribbons and the walls lay straight and parallel. For C-doped ribbons, the domain walls formed a maze domain pattern of grains with c axis normal to the ribbon plane. Scanning electron micrographs showed that a dendrite structure was present in the SmCoZr ribbon surface, and C addition caused the above-mentioned dendrite to diminish. Recently, the melt-spinning technique has been proved to be an additional and feasible way to prepare anisotropic hard magnetic materials.1– 6 A preference for tetragonal c-axis orientation normal to the surface of melt-spun ribbons was observed in the R–Fe–B system.1–4 We have also succeeded in preparing magnetically anisotropic SmCo5 and Sm(CoFeCuZr)Z ribbons with high permanent performance by single-roller melt spinning at low wheel velocities.5,6 The anisotropy was found to be associated with a crystallographic texture formed during the melt spinning process, with the c axis parallel to the longitudinal direction of the ribbons, which is completely different from that of the R–Fe–B system. These results indicated that low wheel speed is helpful to promote the formation of anisotropic meltspun ribbons and the characterization of crystalline texture has a close relationship with the alloy system. SmCo7 phase with the TbCu7 structure has attracted considerable interest for high-temperature application because of its high-temperature performance.7–9 To stabilize this metastable phase and enhance its anisotropy, a small amount of third element, such as Zr, is needed.10,11 The anisotropy field Ha is significantly increased at the expense of the loss of saturation magnetization Ms.10,11 The alloy in the as-cast state shows poor hard magnetic properties and can not be used for permanent magnet
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