Synthesis and magnetic properties of Au-coated amorphous Fe20Ni80 nanoparticles Original Research Article

Gold-coated nanoparticles of Fe20Ni80 (permalloy) have been synthesized by a microemulsion process. The as-prepared samples consist of ∼5 nm diameter particles of amorphous Fe20Ni80 that are likely encapsulated in B2O3. One or more Fe20Ni80@B2O3 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, TB, of ∼33 K. The saturation magnetization, MS, 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, HC, is ∼280 Oe at 5 K.