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.