Positive microemulsion synthesis and magnetic property of amorphous multicomponent Co-, Ni- and Cu-based alloy nanoparticles

Using oleic acid as stabilizer, the monodisperse Co–Ni–Cu amorphous alloys nanoparticles were synthesized by the reduction of CuSO4·5H2O, NiCl2·6H2O and CoCl2·6H2O with KBH4 in positive microemulsion (hexane/sodium oleate/water) system. All results show that the as-synthesized spherical particles are air-stable amorphous alloy nanoparticles in room temperature with the size of 4–7 nm in narrow deviation, and are coated by oleic acid. These amorphous alloy nanoparticles have unique soft magnetic property with small coercivity (Hc) of 7.94 Oe for CuNi, 37.65 Oe for CoCu, 42.17 Oe for CoNiCu and 65.09 Oe for CoNi, respectively. After annealed at 923 K for 0.5 h, the Hc of CuNi, CoCu, CoNiCu and CoNi increased significantly to 46.7, 370.04, 337.4 and 305.5 Oe, respectively. It corresponds to the crystallization of amorphous alloy nanoparticles.