Magnetic Anisotropy of Sm(Co 0.68 Fe 0.22 Cu 0.08 Zr 0.02 ) 7.7 Ribbons Produced by Melt Spinning
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A high degree of texture was observed in melt-spun Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.7 ribbons prepared by single-roller melt spinning at low wheel speed; their easy magnetization axis was parallel to the ribbon plane. Magnetization studies showed an obvious magnetic anisotropy and a 90% higher remanance in ribbons for the field parallel to the longitudinal direction (8.5 kGs) than that for the field parallel to the wide direction (4.4 kGs); this was attributed to a dendritic structure of needle-size grains (2–3 × 10–40 m) with their long axis parallel to the ribbon plane. This texture allowed the development of a new process for producing anisotropic permanent magnets. The domain structure was studied by magnetic-force microscope. A highly ordered and strip-shaped magnetic domain structure was observed on the surface of the ribbons. This was due to the preference for tetragonal c-axis orientation parallel to the surface of melt-spun ribbons. We calculated the domain wall energy ␥ and critical single-domain particle size Dc of Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.7 ribbons.
I. INTRODUCTION
Oriented permanent magnets can be produced by alignment of the hard magnetic phase. This orientation is usually obtained by the powder metallurgy technique1–4: ferromagnetic powdered materials are oriented in a magnetic field and compacted. The pieces are sintered and annealed under appropriate conditions. Most high-energy permanent magnets are produced by this process. Besides the powder metallurgy technique, some other attempts were made to produce oriented magnets by directional solidification5 and solidification in a magnetic field,6 but the process proved to be too complex and was not applied in commercial production. In past years, some efforts were devoted in developing anisotropic melt-spun R–Fe–B ribbons.7–10 A preference for tetragonal c-axis orientation normal to the surface of melt-spun ribbons was observed in the R–Fe–B system.7–10 Recently, we succeeded in preparing magnetically anisotropic SmCo5 ribbons with high permanent performance [(BH)max ⳱ 18.2 MGOe] by single-roller melt spinning at low wheel speeds.11 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 the R–Fe–B system. These results indicate that the melt-spinning method is a feasible way to prepare anisotropic permanent magnetic materials. The 2:17-type Sm(CoFeCuZr)Z magnets, with the highest Curie temperature among the commercial rareearth permanent magnets, have attracted considerable 648
http://journals.cambridge.org
J. Mater. Res., Vol. 17, No. 3, Mar 2002 Downloaded: 02 Apr 2015
interest for high-temperature applications because of their large energy products and high-temperature performance.12–14 In this work, the formation of anisotropic melt-spun Sm(CoFeCuZr) Z ribbons was observed for the first time, and the characterization of their crystalline texture and magnetic properties are repor
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