One-pot synthesis and magnetic properties of hollow Fe₇₀Co₃₀ nanospheres

Hollow Fe₇₀Co₃₀ nanospheres have been prepared in aqueous solution with KBH₄ as the reducing agent and sodium dodecyl sulfonate (SDS) as the stabilizing agent. The diameter of these spheres is about 100–200 nm and the shell thickness is about 15–20 nm. By transmission electron microscopy (TEM) analysis, it was found that these hollow spheres formed via an in situ galvanic replacement reaction between iron nanoparticles and the cobalt cation. These hollow Fe₇₀Co₃₀ spheres exhibit surface plasmon resonance (SPR) absorption in the ultraviolet–visible spectrum. The magnetic properties of the as-prepared hollow Fe₇₀Co₃₀ nanospheres and of a sample annealed at 573 K were studied. Annealing the product can greatly enhance the saturation magnetization M_s and coercivity H_c.