DEVELOPMENT OF HIGH-PERFORMANCE RARE EARTH BONDED MAGNETS

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In the present work, the purpose was to prepare fine magnetic powders of SmィイD22ィエD2FeィイD217ィエD2NィイD2xィエD2-related compounds with good oxidation-resistance as well as excellent magnetic properties and to evaluate the possibility of their practical uses as the raw materials for high-performance anisotropic bonded magnets.First, it was found that SmィイD22ィエD2 (Fe, Co)ィイD217ィエD2NィイD2xィエD2 possesses more excellent intrinsic magnetic property and oxidation-resistance than those of SmィイD22ィエD2FeィイD217ィエD2NィイD2xィエD2. As a result of these properties, high energy product values of (BH)ィイD2maxィエD2>340 kJ/mィイD13ィエD1 were observed on Zn/SmィイD22ィエD2 (Fe, Co)ィイD217ィエD2NィイD2xィエD2 powders as prepared surface-coating with the zinc metal produced via the photo-decomposition of diethyl zinc. Furthermore, the bonded magnets molded from those powders also provided high (BH)ィイD2maxィエD2 values up to 186 kJ/mィイD13ィエD1, and their thermal stability was better than that of the cobalt-free SmィイD22ィエD2FeィイD217ィエD2NィイD2xィエD2-related compounds, together with the oxidation-resistance.On the other hand, metal-bonded magnets were prepared from the SmィイD22ィエD2FeィイD217ィエD2NィイD2xィエD2-related compound powders using In metal or Sn-Zn eutectic alloy as a binder under warm pressing condition. The (BH)ィイD2maxィエD2 values recorded were around 150 kJ/mィイD13ィエD1, which were the highest ones among the figures reported on the similar rare earth metal-bonded magnets. Since the metal binders produced the inter-grain structure between the magnetic powder particles and protected them from water and oxygen in atmosphere, the metal-bonded magnets of SmィイD22ィエD2FeィイD217ィエD2NィイD2xィエD2-related compounds provided excellent oxidation and thermal stability.In addition, new surface-coating method was employed in this work to develop the magnetic ptoperty of the SmィイD22ィエD2FeィイD217ィエD2NィイD2xィエD2-related bonded magnets. This sorption method allowed us to mass-produce the surface-coated magnetic powders.