Figure 2.

Structural and magnetic properties of the FeCo/C nanoparticles. a) TEM image of the 11-nm nanoparticles (scale bar = 20 nm). b) HR-TEM image of the nanoparticles showing the crystalline lattice structure of the FeCo core. c) Powder XRD for the 7- and 11-nm nanoparticles showing the presence of a bcc crystalline core and graphitic shell. d) Raman spectrum (excitation at 632.8 nm) of the 11-nm nanoparticles with single and multiple carbon shells (marked by arrows) showing the D and G bands of graphitic carbon (scale bar = 2 nm). e) Room-temperature magnetization versus applied magnetic field for 11-nm FeCo/C NPs (red symbols) and Fe₃O₄ (black symbols). Note that no hysteresis loop exists owing to the superparamagnetism of the nanoparticles.