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The high-temperature coercivity of mechanically alloyed and subsequently annealed RCo/sub 5/ (R=Sm and Y) is studied. The annealed materials have the hexagonal CaCu/sub 5/ structure with 2:17 (or 1:7) regions as a minor phase. High-temperature magnetic measurements show that the coercivities of materials decrease with increasing temperature from room-temperature to 873 K, but that the temperature coefficient of the coercivity of YCo/sub 5/ is much smaller than that of SmCo/sub 6/. This behavior is explained in terms of the intrinsic temperature variation of the magnetocrystalline anisotropy.

Chemical synthesis is a versatile technique for fabricating novel nanostructured materials. In the Rieke process, a metal salt is reduced by an alkali in a hydrocarbon solvent to form small, highly reactive particles. Synthesis at an elevated temperature (200/spl deg/C) increases the as-synthesized particle size and produces higher coercivities and remanence ratios than observed in similar syntheses at room temperature. The ratio of synthesis temperature to solvent boiling point appears to be an important parameter in both coercivity and oxidation resistance.

Nanocomposite structures composed of ferromagnetic particles dispersed in a matrix are systems in which the magnetic properties can be tailored by varying the size and spacing of the ferromagnetic particles. Nanocomposites of SmCo/sub 5/ in a non-magnetic Nb/sub 0.33/Cr/sub 0.67/ matrix exhibit a wide variety of magnetic properties. SmCo/sub 5/ powder is premilled prior to mechanical alloying. The premilling results in a maximum coercivity of 16 kOe after 2 hours of milling, and an enhanced remanence ratio. Both features may be due to exchange anisotropy and/or exchange coupling between hard and soft ferromagnetic phases. The nanocomposite samples show that, when the SmCo/sub 5/ particulates are small enough, the primary effect of alloying is to disperse them throughout the matrix with no further refinement of size.