TEM picture showing spherical Co NPs with an average size of 12 nm.
XRD spectra of Co NPs after ablation, fragmentation or 1 h annealing at 275 °C in air. The crystalline structure is amorphous after laser ablation or fragmentation and is a crystalline Co3O4 after annealing.
Typical magnetization curve of Co NPs showing superparamagnetism with a saturation magnetization of 27 emu/g.
NPs room temperature (left) and bulk Slater-Pauling5 at 0 K (right) saturation magnetization of Fe, Co, Ni, and their alloys. TM80P20 indicates the magnetization of an amorphous bulk alloy made of 80% transition metal and 20% P.
Saturation magnetization of Co NPs as a function of temperature and the fit for the NPs heated below 400 K computed from the model of Stifler using Eqs. (2) and (3).37
Room temperature hysteresis curve of Co NPs after been annealed at 500 K. The coercive field and the remanent to saturation magnetization ratio are close to those of bulk hcp Co.
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