Ultrafine particles of Fe, Co, and Ni ferromagnetic metals

TLDR

Fe, Co, and Ni ultrafine particles were synthesized by gas‑evaporation in an inert atmosphere, with varying inert‑gas pressures and types, and characterized by XRD, TEM, and magnetic measurements at low and high temperatures. Coercivities of the Fe, Co, and Ni ultrafine particles followed single‑domain theory, reaching 450, 1000, and 1500 Oe for Ni (310 Å), Fe (210 Å), and Co (200 Å) at room temperature, increasing at low temperatures, while saturation magnetizations decreased with decreasing particle size, Co exhibited a face‑centered structure, and some Fe particles appeared amorphous.

Abstract

Fe, Co, and Ni ultrafine particles (UFP) were prepared by a gas evaporation method in an inert atmosphere. The different preparing conditions of the Fe, Co, and Ni UFP included inert gas pressures and kinds were investigated by means of x-ray diffraction, transmission electron microscopy (TEM), and magnetic measurements with low or high temperatures. The experimental results show that coercivities Hc of the Fe, Co, and Ni UFP, depending on particle sizes, obey a single-domain theory. The maximum Hc was 450, 1000, and 1500 Oe, respectively, for Ni (310 Å), Fe (210 Å), and Co (200 Å) at room temperature. The coercivities came up to high in the low temperatures. The saturation magnetizations Ms of the Fe, Co, and Ni UFP decreased with small particle sizes. A face-centered structure of Co UFP (200–300 Å) was confirmed by x-ray diffraction. Some Fe UFP in the shape of balls (200–400 Å) observed in the TEM may be an amorphous structure.