Synthesis and magnetic properties of Au-coated amorphous Fe 20Ni 80 nanoparticles

Abstract

Gold-coated nanoparticles of Fe 20Ni 80 (permalloy) have been synthesized by a microemulsion process. The as-prepared samples consist of ∼5 nm diameter particles of amorphous Fe 20Ni 80 that are likely encapsulated in B 2O 3. One or more Fe 20Ni 80@B 2O 3 particles are subsequently encapsulated in 8–20 nm gold nanospheres, as determined by TEM and X-ray powder diffraction (XRD) line broadening. The gold shells were found to be under expansive strain. Magnetic data confirm the existence of a superparamagnetic phase with a blocking temperature, T B, of ∼33 K. The saturation magnetization, M S, of the as-prepared, Au-coated sample is ∼65 emu g −1 at 5 K and ∼16 emu g −1 at 300 K. The coercivity, H C, is ∼280 Oe at 5 K.