Synthesis And Physical Properties Of SmCo₅ Nanoparticles And Nanoflakes By Surfactant-assisted High-energy Ball Milling

Synthesis and physical properties of SmCo5 nanoparticles andnanoflakes by surfactant-assisted high-energy ball millingMonodispersed permanent magnet nanoparticles have attracted considerable attention in recent years because of their potential application in the high technology industry such as computers, data storage, biomedical technology and remotely controllable Micro-Nanomachine. Due to the superparamagnetism effect, nanocrystalline permanent magnets will lost their coercivity except for several materials with large magnetocrystalline anisotropic constant Ku. SmCo5 material with the highest Ku (2.3×108erg/cm3) among known magnets is the most appropriate candidate for preparation of above-mentioned monodispersed nanocrystalline permanent magnets and can give the lowest thermal limit of particle size down to 2.2 nm.There are physical and chemical approaches for the fabrication of nanocrystalline magnetic materials. The chemical methods, a bottom-up approach, can control the particle's size, geometry quite well, but have had limited success in the synthesis of hard magnetic nanoparticles of rare-transition compounds. Physical approach, a top-down approach, can be used for fabrication of nanoparticles of almost all permanent magnetic material. In this paper, SmCo5 nano/microparticle have been prepared by surfactant-assisted high-energy ball milling.1 SmCo5 nanoparticles have been produced using surfactant-assisted high energy milling. Heptane was used as the milling medium and oleic acid(OA) as the surfactant. High-energy ball milling experiments took place in a milling vial with carbon steel balls by using an SPEX 8000M high-energy ball milling machine. A ball-to-powder weight ratio of 15:1 was used. The amount of surfactant used was 100% by the weight of the starting powder. The sample was milled for 20 h.When surfactant OA was used along with heptane during milling a black liquid was obtained, meaning nanoparticles have been produced and dispersed in the solvent. On the contrary, the solvent remained clear if no OA has been added. Infrared spectroscopy shows that OA has been coated on the surface of nonoparticle. The nanoparticles are 5-10nm in size and shown a poor coercivity of about 2 kOe.2 There are slurry-like sediment in both solvents that added OA or not. When OA was added, the particle in the sediment was flake-like and attach to each other in the flake's thickness direction, forming a closed ring. Such a configuration means the "flake" are oriented and the C axis, namely the easy magnetization direction is perpendicular to the flake's surface. While for the sediment in the solvent without OA adding, the particle shows no anisotropic shape, meaning the surfactant plays a important role in the formation of oriented flake-like particle.3 Besides OA, other two surfactant, oleyl amine(OM) and PVP are also studied. OM influences the formation of suspending of SmCoj nanoparticle and the flake-like particle just like what OA does, while PVP shows no obvious effect.4 When a magnetic field is applied on the rings composed of the "flake", the rings were broken and aligned along the field direction, testifying the perpendicularity of the C axis to the flake's surface.