Preparation of Temperature-Sensitive Rare-Earth–Iron Alloy Fine Particles Using Mechanical Alloying and Sintering

Fine magnetic particles with high saturation magnetization and a large temperature-sensitive magnetization in the temperature range 300–400 K were prepared for use in temperature-sensitive magnetorheological fluids. Two methods, namely high-energy ball milling (HEBM) and sintering followed by HEBM to produce mechanochemical alloys, were used to produce R ₂ Fe ₁₇ component particles. The prepared particles were submicrometer- to micrometer-sized and contained rare-earth–iron alloys and α-Fe phases. Among the prepared particles, Sm ₂ Fe ₁₇ composition powder exhibited the highest temperature sensitivity of −0.02 A m ² kg ⁻¹ K ⁻¹ at 400 K. Furthermore, powders with varying Fe and Sm composition ratios were prepared by sintering and ball milling. The powder prepared from the initial SmFe ₅ composition exhibited the highest temperature sensitivity of −0.32 A m ² kg ⁻¹ K ⁻¹ at 400 K and saturation magnetization was ∼90 A m ² kg ⁻¹ . The powder was composed of SmFe ₅ and Sm ₂ Fe ₁₇ in crystalline, α-Fe phase, and amorphous phase, as revealed by X-ray diffraction analysis and a scanning electron microscope, as well as high-resolution transmission electron microscopy with selected area electron diffraction.